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discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

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Fernald Dose Reconstruction

 Methodology for the Post Special

 Exposure Cohort (SEC) Period, 

 1979-2006

White Paper 

Rev. 2 

National Institute for Occupational 

Safety and Health 

June 23, 2014

Karen Kent, Tom LaBone, Bryce Rich, and Eugene Potter

Oak Ridge Associated Universities Team

- 

Reviewed by Stu Hinnefeld and Mark Rolfes 

Division of Compensation Analysis and Support
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

distribution.

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Overview

This paper provides information on the internal dose assessment methodology 

recommended for performing dose reconstructions for thorium and thoron at Fernald for 

the post SEC period, 1979-2006. 

It is organized into sections and begins with a discussion of the Background information 

relevant to the SECs, followed by the Scope and Introduction. Regulations and Site 

Requirements and Radiological Controls are then presented. The Summary section 

provides the recommendations in table format, followed by a Discussion section, which 

details the recommendations. Example Dose Reconstructions are included to 

demonstrate application of the methods presented in this paper. A Conclusion section 

then follows. Attachments A-G contain supporting documentation and have been 

referenced within this paper. 

Background

Three classes exist for the SEC at Fernald: 

1) All employees of the Department of Energy (DOE), its predecessor agencies, 

and their contractors, or subcontractors who worked at the Feed Materials 

Production Center (FMPC) in Fernald, Ohio, from January 1, 1968 through 

December 31, 1978, for a number of work days aggregating at least 250 work 

days, occurring either solely under this employment, or in combination with 

work days within the parameters established for one or more other classes of 

employees included in the SEC (SRDB Ref ID: 127271). It was determined 

that NIOSH lacked the sufficient information to allow it to estimate with 

sufficient accuracy the potential internal doses from exposure to thorium, which 

employees at this facility may have been subjected (SRDB Ref ID: 129894).

2) All employees of the DOE, its predecessor agencies, and their contractors and 

subcontractors who worked at the FMPC in Fernald, Ohio, from January 1, 

1954, through December 31, 1967, for a number of work days aggregating at 

least 250 work days, occurring either solely under this employment, or in 

combination with work days within the parameters established for one or more 

other classes of employees included in the SEC (SRDB Ref ID: 129226). It 

was determined that NIOSH lacked the sufficient information to allow it to 

estimate with sufficient accuracy the potential internal doses from exposure to 

thorium, which employees working at this facility may have been subjected 

(SRDB Ref ID: 127923). 

3) All employees of the FMPC in Fernald, Ohio, who were not employed by

National Lead of Ohio, NLO, or the Department of Energy or its predecessor 

agencies, who worked at FMPC from January 1, 1951, through December 31, 

1983, for a number of work days aggregating at least 250 work days, occurring 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 3 of 146

either solely under this employment, or in combination with work days within the 

parameters established for one or more other classes of employees included in 

the SEC (SRDB Ref ID: 129226). It was determined that NIOSH lacked the 

sufficient information to allow an estimate with sufficient accuracy the potential 

internal doses from exposure to uranium, which employees of FMPC working at 

this facility may have been subjected. This dose reconstruction infeasibility for 

the period 1951 through 1983 applies only to subcontractors. NIOSH has 

access to an electronic data set that contains the results of the uranium 

urinalysis bioassay program for all the years of FMPC operations, and the 

overwhelming majority of employees of the prime contractor (National Lead of 

Ohio, later named NLO Inc.) have results in the bioassay data set. However, 

the data set does not contain bioassay results for employees of companies 

other than the prime contractor (i.e., non-prime contractor employees). NIOSH 

has obtained a limited number of bioassay samples from non-prime contractor 

employees through data captures, but cannot be certain that all non-prime 

contractor employees’ bioassay data were retained by the site or captured by 

data capture efforts. Additionally, there are some reasons to conclude that the 

prime contractor did not consistently evaluate whether non-prime contractor 

employees should be monitored for radiation exposure because of the 

transitory nature of their work (SRDB Ref ID: 129961). 

FMPC processed thorium intermittently through 1979, using several different chemical and 

physical processes. Additionally, FMPC utilized different monitoring programs for different 

time periods.

The premise of NIOSH’s original proposal for reconstructing internal thorium exposures 

from 1954 -1967 was to use Exposure Studies that characterized exposures to various job 

categories in each building using a time-weighted airborne radioactivity concentration 

value called a daily weighted exposure (DWE). However, later review revealed that the 

daily weighted exposure values were not representative of exposures exclusively from 

thorium operations. The Advisory Board also concluded that such a dose estimate was not 

sufficiently accurate because the dose reconstruction method being proposed could not 

have been based on plausible circumstances (SRDB Ref ID: 127923).

From 1968 to 1978, FMPC used the Y-12 Mobile In Vivo Radiation Monitoring Laboratory 

(MIVRML) to monitor workers’ exposure to thorium. NIOSH proposed to use data from the 

MIVRML to perform dose reconstructions. To do so, NIOSH performed considerable 

research to determine the algorithm that the MIVRML utilized to convert from a given mass 

of thorium to the activity of thorium and its daughters in units of milligrams for the years 

1968-1978. Ultimately, the NIOSH Director and the Board determined that MIVRML 

results expressed as thorium milligrams could not be interpreted with confidence and that 

the reconstructed doses based on such an approach may not be done with sufficient 

accuracy. Therefore, the Board and the NIOSH Director concluded that it was not feasible 

to reconstruct with sufficient accuracy doses from internal thorium exposures for the years 

1968-1978 (SRDB Ref ID: 129894). 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 4 of 146

In vivo examination services were available to all workers at Fernald, including prime 

contractor employees, DOE or DOE contractor employees, subcontractors, or those who 

visited the site to perform work for or, in conjunction with the prime contractor or DOE 

(SRDB Ref ID: 7870, p. 7). Beginning in 1979, the site’s in vivo results were reported in 

terms of activity of Pb-212 and Ac-228. The remainder of this white paper focuses on 

thorium internal dose reconstruction methodology at Fernald, beginning in 1979. 

Scope

The scope of this paper is limited to the internal thorium dose reconstruction methodology 

for the post SEC period (1979 - 2006). Thoron exposures are included. Internal 

exposures to uranium are beyond the scope of this paper, and, are not included in any 

further discussions, with the exception of customized breathing zone air monitoring results, 

which include uranium. 

Introduction

According to a timeline of thorium processing operations (SRDB Ref ID: 42940), thorium 

processing began at Fernald in 1954 and continued through 1979. Fernald was the 

national thorium materials repository for the DOE starting in 1972. In 1988, an 

environmental assessment indicated that the inventory of thorium materials at Fernald 

consisted of approximately 1,100 metric tons (as thorium) of various thorium compounds. 

In 1988, the Plant 8 silo and bin contained approximately 175 metric tons of bulk thorium 

oxide materials plus other inert materials. The remainder of the thorium inventory was 

stored in various size containers in Warehouse Buildings #64, 65, 67, and 68 and as 

thorium nitrate in Tank 2 at the Pilot Plant. A small number of drums were in outside 

storage adjacent to Building #65 (SRDB Ref ID: 4611, p.10). The following table 

summarizes Fernald’s stored inventory of thorium in 1987 (SRDB Ref ID: 84457, p. 3). 

Location Quantity Weight 

Plant 8 Silo and Bins Bulk thorium oxide material & 

other inert materials 

175 metric tons

Pilot Plant Tank 2 Thorium nitrate solution 9 metric tons

Building 64 (Plant 9 WH) 181drums 64.2 tons

Building 65 (Plant 5 WH) 5599 drums 1246.3 tons

Building 67 (Plant 1 Storage Bldg) 5992 drums 213.5 tons

Building 68 (Pilot Plant WH) 1317 drums 485.7 tons

PAD West of Building 65 212 (240 overpacked) drums 52.5 tons

WH = Warehouse

This includes a total of 13,329 drums and 2062.2 tons of thorium material (SRDB Ref ID: 

84398, p. 13), plus the Plant 8 silo and bins material and the thorium nitrate solution in the 

Pilot Plant tank.

Various documents exist that discuss Fernald’s thorium inventory and processing

including, but not limited to: SRDB Ref ID: 29071, 84398, 84457, 85069, 83668, 41375, 

44266 and 9012.
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 5 of 146

Post SEC Regulatory & Site Requirements 

Implementation of DOE Order 5480.11, Radiation Protection for Occupational Workers, 

was the requirement document beginning January 1, 1989, with compliance required 

January 1990. This replaced DOE Order 5480.1A. Sites were required to submit a status 

report to DOE by January 27, 1989 with requests for exemptions and an implementation 

plan detailing how compliance would be achieved by December 31, 1989, (i.e., full 

compliance was not required until December 31, 1989), unless the implementation plan 

specified an earlier date (SRDB Ref ID: 108238, p. 5). 

In June 1992, the DOE Radiological Control (RadCon) Manual was published and, in April 

1994, Revision 1 of the DOE RadCon Manual occurred. DOE Order 5480.11 was 

cancelled September 29, 1995 and DOE required that each site develop their own 

Radiological Control Manual. Initially, the RadCon Manual was a guidance document, and 

later, a requirement. Fernald’s Radiological Control (RadCon) Requirements Manual, Rev 

0 was issued with an effective date of December 31, 1994 (SRDB Ref ID: 3269, p.3). The 

final rule for 10 CFR 835, Occupational Radiation Protection, occurred in January 1993 

and became effective December 14, 1993; however, full compliance wasn’t required until 

January 1, 1996. 

In the site’s Technical Basis for Workplace Air Monitoring Manual, Rev. 0, (August 1995), it 

was recognized that a technological shortfall existed in Fernald’s internal dosimetry 

program with respect to thorium bioassay monitoring methods. It stated, “In the case of a 

technology shortfall, an enhanced workplace monitoring program shall be instituted to alert 

Radiation Protection personnel of areas with the potential to exceed 2 percent of the 

Annual limit of Intake (ALI) per 10 CFR835.403, based on contamination levels and 

potential release points” (SRDB Ref ID: 3545). 

The Derived Air Concentrations (DACs) for Th-232 in DOE 5480.11 were the same as 

those listed in 10 CFR 835, namely 5E-13 μCi/ml (Class W) and 1E-12 μCi/ml (Class Y), 

(SRDB Ref ID: 108238, p. 63 and 32003, p. 3). 

Post Production Thorium Activities

An inventory of thorium production orders shows that there were no orders after 1985 and 

only a few from 1979 -1985 (SRDB Ref ID # 9012). It is likely that most or all of these 

production orders involved just taking stored material out of a warehouse and shipping it to 

a customer. The occasional thorium repackaging effort (which typically involved placing 

eroding containers into larger containers) would have been short-duration, involved very 

few individuals, and those individuals were likely undergoing in vivo monitoring for 

potential uranium exposure during this period, so they would have had in vivo results. 

In 1987, an environmental assessment for Fernald proposed the repackaging, overpacking

and shipment of the thorium materials. The purpose of the proposed action was to 

stabilize deteriorating containers of thorium, and move the thorium from the site for long 

term retrievable storage under more appropriate conditions. Over the years of storage at 

Fernald, the environment had caused deterioration of the drums and containers, as well as 

the warehouses in which the material was stored (SRDB Ref ID: 4611, p.13). The 1987 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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environmental assessment identified 212 drums containing 241 smaller containers of 

thorium material stored outside of Building 65 and more than 13,000 containers stored in 

warehouse buildings #64, 65, 67, and 68. An estimated 175 metric tons of thorium 

material was in the Plant 8 bin and silo storage; it was estimated that approximately 2500 

205-liter drums or 400 double walled boxes would be generated during removal (SRDB 

Ref ID: 4611, p.15). 

Therefore, thorium work after processing ended at Fernald would have primarily been 

associated with efforts included in the “Three Project Plan,” which involved improving the 

temporary storage conditions for thorium (SRDB Ref ID: 3559, p. 203). The total thorium 

inventory from the three projects was equivalent to approximately 15,000 fifty-five gallon 

drums (SRDB Ref ID: 85069, p. 4). The result of the three project plan was that thorium 

containers of material were repackaged and/or overpacked to meet retrievable storage 

criteria and Department of Transportation (DOT) shipping requirements. The thorium 

materials were then shipped to the Nevada Test site (NTS) retrievable storage facility

(SRDB Ref ID: 4611, p.12). 

Project 1

A detailed task force report on the thorium silo remediation/thorium material disposition 

was generated in 1986 (SRDB Ref ID: 28862). An Environmental Assessment on thorium 

handling was developed in 1987 (SRDB Ref ID: 29077). The first project addressed the 

bulk thorium materials in the Plant 8 silo and bins and was subcontracted to International 

Technology (IT) in September 1987. The timeframe for when actual work was being 

performed was November 1988 - March 1989. IT’s scope of work included: 

Design/Installation/Operation of the Thorium Removal System, Plant 8 Silo and Bins 

Thorium Removal, and Packaging and Decontamination and Decommissioning of Plant 8 

Thorium Handling System and Plant 8 Roof Refurbishing (SRDB Ref ID: 33877 & 29071). 

In September 1987, Fernald began the design and construction of the handling system 

necessary to remove and package the bulk thorium materials. Following construction, the 

removal, handling, and packaging of thorium began in November 1988. As the bulk 

materials were removed from the silo and bins, they were placed in double containment 

drums called overpacks (a 48-gallon drum is packaged inside a 55-gallon drum), 

inventoried and monitored. The drums were then stored in a new onsite warehouse 

located along the northern edge of the production area, away from daily plant operations. 

The overpacking portion of the project was completed in March 1989. The silo and bins 

were then to be decontaminated and demolished (SRDB Ref ID: 3554, p. 451). 

Project 2

The second project involved the overpacking of the 241 containers (212 of the containers 

were drums) stored outdoors. The actual work was performed January - May 1990. As 

part of the second project, the design of a remote system for handling, identifying and 

overpacking the thorium drums and containers stored in warehouses and outdoors was 

completed in 1988. Purchase of the overpacking equipment began in early 1989. The 

training for this project was conducted August - December 1989 and included a variety of 

workers, such as: chemical operator, pipefitter, welder, electrician, oiler, millwright, 

radiation safety technician, industrial hygiene technician, maintenance supervisor, 

instrument mechanic, industrial mechanic, electrical maintenance supervisor, schedule 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

distribution.

 Page 7 of 146

analyst, safety engineer, safety and fire inspector, senior project engineer, planner 

estimator, and various technologists, technicians, supervisors (SRDB Ref ID: 44282). 

Each container was inventoried, weighed and scanned (to determine the percentage of 

thorium it contained), then placed in interim storage at Fernald (SRDB Ref ID: 3554, p. 

451). This project was expected to be completed in March 1990; however, due to 

temperature restrictions and equipment malfunctions, completion of thorium overpacking 

did not occur until May 1990. As of April 30, 1990, one hundred seventy-five drums of 

thorium had been overpacked (SRDB Ref ID: 33893, p. 14). 

Project 3

The third project involved the overpacking of 13,000 containers of thorium, which began in 

1991. Project 3 was planned for 1991 - end of 1993. However, it was not completed as 

scheduled, leaving 5,600 drums to be over packed, as discussed below. The timeframe of 

this project was approximately 1991-2006. An evaluation for the thorium storage buildings 

was conducted in 1991, and identified that the Building 65 containers were in a severe 

state of deterioration with resultant leakage of material. This resulted in the evolution of 

the Thorium Overpacking Project (TOP), which was to safely and effectively overpack 

approximately 5,600 drums of thorium bearing materials into approved strong, tight 

containers in preparation for off-site shipment for final disposal at NTS. For the purposes 

of this paper, the TOP is considered to be a continuation of Project 3. The drum 

overpacking was accomplished through the implementation of a Remote Controlled 

Material Handling System (RCMHS) which included a mobile unit fitted with appropriate 

controls for remote operation, remote control command unit, handling attachments and 

visual monitoring system (SRDB Ref ID: 130104). On July 28, 1991, the overpacking and 

relocation of 35 thorium containers characterized as mixed waste to a RCRA warehouse 

was completed. Also completed were the necessary overpacking, relocation, and RCRA 

evaluation actions for all but 16 of 192 containers which required further characterization. 

The characterization of the 16 remaining containers was scheduled to be completed by 

June 1992 (SRDB Ref ID: 3559, p. 90, 202-203). Between January 1, 1992, and April 1, 

1993, more than 1,600 drums of thorium materials were shipped to NTS (SRDB Ref ID: 

3569, p. 81). Overpacking in the Thorium Warehouse was completed in 1992. Also, 

thorium was repackaged and transferred to the (Old) Plant 5 Warehouse in the same year. 

Note that the Thorium Warehouse being discussed at this point is Building 64 and the 

building referred to as the (Old) Plant 5 Warehouse is Building 65 (SRDB Ref ID: 4611, p. 

24 and 3563, p. 174). These movements were done to lower radiation exposures to site 

workers since fewer personnel entered the areas of the (Old) Plant 5 Warehouse. Plans 

were underway to consolidate all thorium into this warehouse pending approval for

shipment to NTS (SRDB Ref ID: 3563, p. 178). 

Overpacking in the Plant 1Thorium Warehouse was completed in 1993. The Pilot Plant 

Warehouse overpacking efforts were completed in 1992. The FEMP proposed to complete

the overpacking in the (Old) Plant 5 Warehouse by the end of 1993 (SRDB Ref ID: 3563, 

p. 178). In 1993, three drums of thorium materials were shipped to NTS. Also in 1993, the 

site completed the overpacking of 6,100 drums of thorium materials and expected to have 

approval to ship those materials to NTS in 1994 (SRDB Ref ID: 3569, p. 81). 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

distribution.

 Page 8 of 146

In 1994, the site shipped 750.4 drum equivalents of thorium material to NTS for disposal. 

Additional shipments were planned for 1995 (SRDB Ref ID: 3575, p. 91).

Almost 6,000 gallons of thorium nitrate, a contaminated acid waste stream, were treated 

and solidified safely in 1995. The final rinse of the thorium nitrate tank was completed 

November 9, 1995, less than two months after Chem-Nuclear, Fernald’s subcontractor, 

began processing the material and six months after Fernald and Chem-Nuclear began 

designing the treatment system. During the project, 369 drums of solidified thorium cement 

were generated (SRDB Ref ID: 3578, p. 41). In 1995, the site shipped 776 drum 

equivalents of thorium material to NTS for disposal (SRDB Ref ID: 3578, p.104) 

Fluor Daniel Fernald workers began packaging the remaining 5600 thorium drums from 

Project 3 on May 6, 1996. The project established multiple safety guidelines and 

compliance requirements to ensure safe operations and the safety of the workers. The 

project was more than halfway to the target to overpack 5,600 deteriorated drums of 

thorium for safe transportation and permanent, off-site disposal. 

As of April 1, 1997, an estimated 4,489 drums had been overpacked. The two-year 

operation, targeted for completion in September 1997, was ahead of schedule. DOE and 

Fluor Daniel Fernald anticipated the project would be completed in the summer of 1997. 

The disposition of thorium was an ongoing effort since June 1992 (SRDB Ref ID: 3586, 

pg. 26). In 1996, Fernald shipped 2,172 drum equivalents or 46,101 cubic feet of thorium 

material to NTS (SRDB Ref ID: 3586, p. 93). In 1997, Fernald removed 3,400 containers 

of thorium material and shipped 10,875 drum equivalents, or 80,480 cubic feet of thorium 

material to NTS, completing the Thorium Overpack Project (TOP). Characterization of the 

remaining estimated 8,500 containers of thorium legacy waste at the site was initiated in 

1997 (SRDB Ref ID: 3592, p. 54). The characterization documentation and formal RCRA 

waste determinations for the remaining estimated 8,500 containers of thorium legacy 

waste continued in 1998 (SRDB Ref ID: 3604, p. 51). 

Plant 9 decontamination and dismantlement was completed in 1999. The subcontractor 

completed field work in February, including structural steel size reduction, 

decontamination, and demobilization. The project closeout report was submitted to the

regulatory agencies and approved. The characterization documentation and formal RCRA 

waste determinations for the remaining estimated 8,500 containers of thorium legacy 

waste continued in 1999 (SRDB Ref ID: 3606, p.47, 52). 

In 2000, over 6,000 of these containers were shipped to NTS (SRDB Ref ID: 9010, p. 47). 

Through the end of 2001, over 6,400 of these containers were shipped to NTS (SRDB Ref 

ID: 3516, p. 44). Through the end of 2002, over 7,100 of these containers were shipped 

to NTS (SRDB Ref ID: 126955, p. 51). Through the end of 2003, over 8,400 of these 

containers were shipped off-site for treatment, with subsequent disposal at NTS. Those 

containers included all RCRA hazardous thorium legacy-waste that had a scheduled 

milestone of December 5, 2003. This shipping effort removed approximately 1,500,000 

pounds (681,000 kg) of thorium from the total site thorium inventory (SRDB Ref ID: 

126956, p. 51). In 2004, Fernald shipped 4,274 pounds (1,940 kg) of mixed thorium waste 

to Envirocare of Utah, Inc. for treatment and disposal, and 21,192 pounds (9,621 kg) of 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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non-hazardous thorium waste to NTS for disposal. At the end of 2004, there were only a 

few containers of thorium waste remaining on site (SRDB Ref ID: 129790, p. 45). In 

2005, Fernald shipped 1,051 pounds (477 kg) of mixed thorium-contaminated oil to 

Envirocare of Utah, Inc. for treatment and disposal. At the end of 2005, there were only 

three containers of thorium-contaminated mixed waste remaining on-site (SRDB Ref ID: 

129791, p. 48). With the completion of remediation, DOE completed the disposition of the 

containerized waste inventory. The last shipment of hazardous waste occurred October 2, 

2006, ending hazardous waste management activities (SRDB Ref ID: 129793, p. 57). 

Remediation of the Fernald site was completed on October 29, 2006, and the site was 

officially transferred into Legacy Management on November 17, 2006. The DOE’s Office 

of Legacy Management and their Technical Assistance Contractor, S.M. Stoller 

Corporation, assumed full responsibility for operations at the Fernald site on November 17, 

2006 (SRDB Ref ID: 129793, p. 15, 20).

Radiological Controls

The documentation from Projects 1, 2 and 3 demonstrate that the radiological protection 

program included the elements of today’s standards. Procedures associated with thorium 

handling, training plans and rosters exist. Detailed technical reviews were conducted and 

adequate control measures appear to have been implemented. Memos describing events 

from daily thorium operations were reviewed. Radiological controls described within these 

documents include requirements for work permits, respiratory protection, shielding 

requirements, personal monitoring, bioassay, air monitoring requirements, etc. As Low As 

Reasonably Achievable (ALARA) principles were utilized. 

The post SEC thorium processes appeared to be well planned and designed to minimize 

exposure to workers with adherence to regulatory requirements and the standards of the 

era. A detailed timeline of Fernald’s post-production thorium activities is summarized in 

Attachment A. 

Some examples of controls from Project 1 are:

Operational Safety Requirements (OSRs) for the removal of thorium handling system

required that all radiological monitoring equipment be tested and calibrated before work 

began and to be recalibrated semiannually. In addition, Breathing Zone (BZ) air sampler 

pumps were required to be calibrated daily (SRDB Ref ID: 33881, p.25).

A Technical Summary of the Thorium Handling Project (SRDB Ref ID: 33896, p. 41) 

discusses that IT’s BZ samples will be collected for a suitable duration to achieve the 

detection limits equal to the derived concentration guide specified for Thorium-232 and its 

daughter products in DOE Order 5480.11 and its revisions. 

Thorium Repackaging Project included a review of IT’s Radiological Safety Program due 

to a suspected thorium inhalation event (SRDB Ref ID: 33877).

A “Minor Event Report” of a thorium spill at the Plant 8 thorium silo, contamination survey 

and air monitoring report was documented (SRDB Ref ID: 33879). 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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 Page 10 of 146

IT generated a memo discussing problems associated with an open duct on the top of the 

Plant 8 thorium bin (SRDB Ref ID: 33880).

Some examples of controls from Project 2 are: 

Memorandum of an Air sampling counting procedure associated with thorium repacking in 

1989 (SRDB Ref ID: 33954) and another Memorandum on the Summary of Radiological 

Controls used in thorium repacking, 1990 (SRDB Ref ID: 33882). 

OSRs for the removal and overpacking program (212 containers of thorium metals) in 

1989 (SRDB Ref ID: 33959). 

Various Standard Operating Procedures (SOPs) for thorium overpacking in 1989, including 

thorium drum handling procedures (SRDB Ref ID: 44281). Other SOPs and checklists 

associated with the thorium handling project in 1989 (SRDB Ref ID: 44272 through 

44280). 

Training plan for thorium overpacking of 212 drums (SRDB Ref ID: 44290). 

Final Safety Analysis Report (FSAR) for thorium overpacking of 212 drums, 1989 (SRDB 

Ref ID: 4188). 

In the SOP Radiological Controls for Repackaging Thorium, Rev 1, March 1990, the DAC 

for thorium-232 was noted to be 5.0x10-13 uCi/ml, also, “Before, at three month intervals 

during and at completion of the job, individuals working with thorium shall have in vivo lung 

measurements performed. Individuals whose work includes routine handling of thorium 

shall be required to submit background fecal samples prior to initiating work. Air sample 

results indicating a thorium inhalation in excess of 8 DAC hours (with the respiratory 

protection factor considered) shall trigger in vivo measurement and/or bioassay. 

Additional bioassay (including urine or fecal analysis) may also be required as determined 

by the responsible Radiological Engineer until the magnitude of the intake has been 

estimated, the individual may be restricted from Airborne Radioactivity Areas” (SRDB Ref 

ID: 33913). 

Radiation exposure to workers during thorium operations was planned to be covered in a 

radiological safety work plan. Administrative controls for occupational exposure included 

personal dosimetry, health physics surveys, radiation protection procedures, and the use 

of protective clothing and respiratory protection, as required. These controls would limit 

radiation exposure to workers to as low as reasonably achievable within the DOE limit of 

five rem per year. The estimated whole body dose equivalent to the maximum individual of 

the public who resided at the site boundary at the point of maximum annual concentrations 

of thorium-232 was calculated to be 3.8x10-3 millirem in an environmental assessment. 

The same assessment determined that the total calculated dose equivalent to the 

maximum individual of the public using the 65-week life of the project was 4.9x10-3

millirem, with a committed dose equivalent to the bone surface of 3.4 millirem (SRDB Ref 

ID: 4611, p.55-57). Air samples were planned to have been collected during repackaging 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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operations to document that personnel exposures were acceptable (SRDB Ref ID: 4611, 

p.20). 

Some radiological controls identified in a 1990 memorandum on the thorium repackaging 

project were: “A new radiation work permit is required at the beginning of each shift. 

Access to the thorium repacking area will be controlled by an access control list. Only 

those who have completed thorium training will be allowed in the repackaging area. Each 

thorium operator is required to wear a BZ sampler at all times while he is inside the

radiological barrier fence. Personnel who work inside the thorium repackaging area for

greater than 30 minutes per day are required to wear an airline hood. Those who work for 

30 minutes or less are required to wear a full-face respirator. The forklift operator is 

required to wear a PAPR half-face respirator while he operates the forklift. Personnel who 

enter the repackaging area must wear anti-C clothing complete with shoe covers, hood, 

and gloves which are taped at the wrist and the ankles. Background in vivo samples and 

fecal samples were taken for each operator prior to starting the operation and at three

month intervals during the operation” (SRDB Ref ID: 33882). 

The Fernald Internal Dosimetry Technical Basis Manual, December 31, 1990, states “The 

major potential source of exposure to thorium material at the FMPC is the repackaging of 

thorium drums. This operation is covered under the safety procedure, “Radiological 

Controls for Repackaging Thorium. All compounds of thorium at the FMPC are assigned 

to inhalation class Y" (SRDB Ref ID: 4145, p. 47, 48).

Some examples of controls from Project 3 are:

Radiological Controls for the Thorium Nitrate Solidification & Stabilization Project (draft) 

gave consideration to maintaining airborne radioactive material concentrations below 

maximum values of 0.1 DAC in the breathing zone of workers, with thorium-232 (Class W) 

identified as the radioisotope of concern for occupational radiation protection purposes. 

The DAC for Class W Th-232 is 5x10-13 μCi/ml, as listed in Appendix A of 10 CFR 835. 

Posting as an "Airborne Radioactivity Area" was required at 10% of this DAC. In addition 

to the monthly urine sampling requirement for this project, a base-line fecal sample was 

required of all personnel whom must enter the zone. Personnel Air Sampling (PAS) was 

required for all personnel whom must enter the zone (SRDB Ref ID: 32604). 

Transmittal of Final Report for Thorium Nitrate Tank indicated that the DAC for Thorium232 (Class W soluble) was applied for radiation protection purposes on this project. In 

addition, from Appendix A of 10 CFR 835, a DAC of 1.0 working level (WL) was applied for 

thoron progeny (SRDB Ref ID: 36159).

Information on Removal Action No. 9 Building 65 Thorium Overpacking Project (SRDB Ref 

ID: 130104). 

Safety Analysis Report for the Warehoused Thorium Overpacking Building 65 (SRDB Ref 

ID: 3503).
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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Numerous documents exist which detail the planning involved in the thorium work, the 

follow-up, and the involvement of Radiological Controls from Project 3. Some of these

documents include, but are not limited to a “Health Physics Plan for the TOP,” Rev 2

(SRDB Ref ID: 132927), a memorandum on the “Updated Dose Estimate for the TOP” 

(SRDB Ref ID: 132929), and an “Airborne Contamination Control Implementation Plan for 

the TOP,” Rev 2 (SRDB Ref ID: 132930). 

“Note that the HIS-20 database was not implemented until the mid-1990s. Although 

thorium BZ samples were being collected as indicated in the control descriptions above, 

they are not reliably available in HIS-20 until 1995. However, in-vivo results for thorium 

workers are available for Thorium Overpacking Projects 1, 2, and 3.”

Summary

The major Fernald thorium work and regulatory requirements post SEC period can be 

summarized as:

Project Project Description Timeframe Regulatory 

Requirements

1 Overpacking Plant 8 and Silo 

thorium material

November 1988 -

March 1989

DOE 5480.11

DOE 5480.1A

2 Overpacking 241 containers 

(212 were drums)

January 1990 - May 

1990

DOE 5480.11

3 Overpacking 13,000 containers 1991 - 2006 DOE 5480.11

RadCon Manual

10 CFR 835

Thorium doses are recommended to be assigned as follows at Fernald: 

Timeframe

In Vivo Data Exist 

(Yes/No)

Evaluation Method Source/Basis

1979 - 1994 Yes In Vivo Results aLaBone documents

1979 - 1989 No Coworker Data bThorium In Vivo 

Coworker Study

1990 - 1994 No 10% Th-232 Class 

W DAC

c

Thorium Inh/Ing 

intake from air limit 

calculation (DOE 

5480.11 & Project 2 

documentation)

1995 - 2006 Yes - may use to 

decide if in vivo 

results reflect a lung 

burden that had 

been previously 

BZ Air Monitoring 

results

10 CFR 835 

compliance and 

thorium bioassay 

technology shortfall

(SRDB Ref ID: 3545 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

distribution.

 Page 13 of 146

identified from 

earlier exposure. 

Positive in vivo is 

used in place of

negative BZ results

unless it is an 

artifact of an earlier 

detected lung 

burden. For in vivo 

results below MDA 

use BZ results.

No – use BZ data

& HIS-20 database)

a. Evaluation of Fernald Ac-228/Pb-212 Chest Count Data, 04/18/2013, Activity

Ratios for various types of Thorium, 06/21/2013, Approximate Evaluation of Pb-212 

Chests Counts Following Intakes of Thorium, 07/19/2013, and Using Ac-228 and 

Pb-212 to Measure Intakes of Th-232, 09/18/2013, see Attachments B.1-4.

b. Thorium In Vivo Coworker Study (in development), Attachment C. 

c. Thorium Inhalation/Ingestion intake from air limit calculation, Attachment D 

The basis for these recommendations is described below, with the timeframes separated 

out. 

Discussion

1979-1994

Chest count measurements exist in claimant’s records during this timeframe and may 

extend beyond this timeframe. The evaluation of in vivo results uses ORAUT-OTIB-0060, 

“Internal Dose Reconstruction” (SRDB Ref ID: 29984) methods. If all in vivo results are 

negative, then only missed dose is assigned. Positive in vivo results are adjusted for bias 

by subtracting the bias values in the table below. The most claimant favorable absorption 

type is assumed. 

The radionuclides that can be quantified with a chest count are Ac-228 and Pb-212. 

Thorium intakes are evaluated using Pb-212 values rather than the Ac-228 results

because the Pb-212 results are considered more reliable for the calculation of Th-232 and 

Th-228 dose. The chemical separation history is normally unknown, therefore the default 

worst case material composition (triple-separated thorium with a Th-228:Th-232 

disequilibrium ratio of 0.19:1) is assumed. 

Detection Levels (DLs) were derived from Attachment B-1, Evaluation of Fernald Ac228/Pb-212 Chest Count Data, 04/18/2013, as summarized below. 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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a

Summary of Bias and DL for Ac-228 and Pb-212 (nCi) in Chest

Year Pb-212 Bias Pb-212 DL Ac-228 Bias Ac-228 DL

1979 -0.014 0.156 0.031 0.169

1980 -0.045 0.123 0.025 0.091

1981 -0.056 0.108 0.022 0.127

1982 -0.058 0.121 0.010 0.117

1983 -0.101 0.122 -0.008 0.097

1984 -0.089 0.111 0.001 0.079

1985 -0.086 0.117 0.017 0.102

1986 -0.085 0.128 0.020 0.114

1987 -0.047 0.123 0.008 0.106

1988 0.002 0.181 0.058 0.107

1989-1994b 0.072 0.21 0.182 0.55

a. DLs are equal to one-half of the Minimum Detectable Activity (MDA).

b. The basis for these values is described in SRDB Ref ID: 131224. 

The in vivo results are evaluated using the following methodology:

1. Evaluate the Pb-212 chest burden (MDA/2 for missed or result adjusted for bias for 

fitted dose) with a Th-228 biokinetic model in IMBA. Use the annual DLs from the 

table to evaluate missed dose. 

2. Multiply the calculated Th-228 intake rate by a correction factor of 1.1 (as 

applicable) and assign it as the intake rate of Th-228.

3. Divide the estimated Th-228 intake rate by 0.19 (based on the Th-228:Th-232 ratio 

of 0.19:1) to obtain the Th-232 intake rate. Since the thorium is assumed to be 

triple-separated, there is no associated Ra-228 with the thorium intake.

4. Evaluate the Ac-228 chest burden (MDA/2 for missed or result adjusted for bias for 

fitted dose) with a Ra-228 biokinetic model in IMBA and assign it as the intake rate 

of Ra-228. Note that since this is unsupported radium, it is not part of a mixture 

and therefore only assessed as absorption type M.

Notes to consider

The correction factor of 1.1 (based on the Th-228 approximation method) does not apply 

to underestimates. For overestimates, the 1.1 correction factor is applied. In order to 

apply the 1.1 correction factor, chronic intakes must be longer than 1 year and acute 

intakes must have the chest count taken more than 30 days after the intake. For best 

estimates, or if either of the time period scenarios are true, then a best estimate of the 

correction factor must be determined.

For best estimates of dose, Dose and Risk Calculation (DCAL) software is used to account 

for the independent kinetics of the thorium decay chain and the loss of Rn-220.

DLs from the table are used to evaluate chest count measurements, unless claim-specific 

chest count DLs exist.

Triple-separated thorium with a ratio of 0.19:1, Th-228:Th-232 is assumed, unless claimspecific information exists. For triple-separated thorium, there is no Ra-228 intake 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

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 Page 15 of 146

associated with the thorium intake. However, there is likely unsupported Ra-228 (not part 

of the thorium mixture) which is evaluated separately, as discussed in #4 above. 

It is recognized that the assignment of thorium missed dose based on in vivo counts will 

result in high doses, which NIOSH doesn’t believe occurred given the radiological controls 

in place at the time. 

The assignment of thorium doses based on in vivo results includes the IT subcontractors 

who were involved with Plant 8 silo and bin remediation/thorium drumming (Project 1), 

which ended March 1989. 

1979 -1989 

All thorium workers should have in vivo results, as they were required by the site. 

However, in the unlikely event that no in vivo results exist for a thorium worker, then 

coworker intakes will be assigned. The basis for the coworker intakes will be described in 

Attachment C, Thorium In Vivo Coworker Study (in development). Although the actual 

intake values are in development, the values in the table below are shown as proof of the 

coworker concept to represent the chronic exposures that thorium workers would have 

received. 

The derived thorium coworker intakes represent the 50th percentile. 

1979 -1989 Thorium-232 intakes, (pCi/day)d

Period Type M b GSDc Type Sb GSDc

1979 13.2 3.60 0.220 7.04

1980-1988 1.01 7.95 0.220 7.04

1989 a 1.01 7.95 0.220 7.04

a. Data from 1980 through 1988 are extrapolated to 1989. The thorium processes at 

Fernald were unchanged between 1988 and 1989.

b. A comparison of absorption type by organ is made and the absorption type resulting 

in the highest dose is assigned.

c. GSD = Geometric Standard Deviation.

d. These intakes do not represent the finalized values, actual values are in 

development.

Triple-separated thorium with a ratio of 0.19:1, Th-228:Th-232 is assumed for coworker 

intakes. For triple-separated thorium, there is no Ra-228 intake associated with the 

thorium intake. 

Thorium workers include: Chemical operators, fork truck drivers, laborers, transportation 

laborers, operations, production workers and maintenance personnel. Subcontractors 

from IT Corporation in 1988-1989 should be assumed to be thorium workers unless there 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 16 of 146

is evidence to the contrary. Only one IT claimant has been identified in NIOSH OCAS 

Claims Tracking System (NOCTS). That individual has in vivo counts showing less than 

detection Th-232 results near the start and termination of employment. This provides 

some confidence that IT Corporation workers can be identified and that DOE records can 

be provided for them.

1990-1994 

Thorium workers with no in vivo results, but with pre-job fecal sample results during this 

employment period at Fernald are recommended to be assigned a dose based on a 

thorium air concentration of 5x10-14 μCi/ml (10% DAC), as a maximum potential exposure. 

The documentation for Project 2 (January 1990 - May 1990) shows the emphasis on air 

sampling and appeared to be a well-planned and thorough program. Pre-job fecal 

samples were taken, but not many follow-ups, likely indicating that things went 

smoothly. The BZ samples must have been filed with the project and never made it into 

HIS-20, as the earliest thorium samples in the HIS-20 database appear in 1993, with not 

many until 1995. 

With the implementation of DOE Order 5480.11, ambient air monitoring was required in 

occupied areas with the potential to exceed 10% of any of the DAC values given in 

Attachment 1 of the order (SRDB Ref ID: 108238, p. 26). The values in Attachment 1 

were the same DACs as in the 10 CFR 835 final rule, Appendix A. The access points to 

any area where airborne radioactive material concentrations exceeded 10% of the DACs 

in Attachment 1 were required to be clearly and conspicuously posted with a sign that 

identified the radiological area as an "Airborne Radioactivity Area" (SRDB Ref ID: 108238, 

p. 31). All radiological areas were required to have an appropriate entry control program 

to ensure that personnel entry into the radiological areas was controlled (SRDB Ref ID: 

108238, p. 31).

Internal dose evaluation programs were required for radiation workers exposed to surface 

or airborne radioactive contamination where the worker could receive 0.1 rem annual 

effective dose equivalent from all intakes of all radionuclides from occupational sources, or 

if any organ or tissue dose equivalent could exceed 5 rem annual dose equivalent (SRDB 

Ref ID: 108238, p. 26). Note that the monitoring requirement was based on annual dose 

equivalent instead of committed dose until the implementation of the RadCon Manual in 

1992. However, since the determination was prospective, this distinction is not important. 

Fernald recognized that thorium overpacking operations required internal dose monitoring 

and evaluation. The implementation of the DOE 5480.11 requirements by January 1990 is 

readily apparent from the site documentation of the thorium overpacking work (access 

control, respiratory protection requirements, air monitoring with general area and BZ 

samples, and pre-job and follow-up fecal samples, if required). This provides confidence 

that no thorium workers were exposed to greater than 10% of a DAC (respiratory 

protection being taken into account) on a sustained or average basis.

Since the thorium overpacking procedures did not appear to change much over time, it 

was considered useful to compare the thorium BZ results from the later periods to the 10% 

of a DAC assumption proposed for 1990 - 1994. The total annual thorium exposures in 

DAC-hrs from 1993 - 2006 in the HIS-20 database were fit to a lognormal distribution. The 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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geometric mean of the results without the respiratory protection factor did not exceed 17 

DAC-hrs/yr for any of the three data-weighting methods. This is much less than 0.1 DAC 

times 2000 hrs/yr (200 DAC-hrs/yr) which would be the upper bound. With respiratory 

protection factors applied, the 95th percentile of the BZ results did not exceed 14 DAChrs/yr for any of the three data-weighting methods.

Therefore, the usage of 10% of the thorium DAC limit (5 E-14 μCi/mL) provides a sound 

basis for this calculation. The thorium dose is based on the assumption of 100% Th-232, 

as the most claimant-favorable radionuclide. An inhalation and ingestion Th-232 intake is 

assumed. Although the thorium exposure in 1990 could be limited to January - May (5 

months of project 2 work), 2000 hours/year was assumed in this calculation for 1990 -

1994, as a claimant favorable measure. A breathing rate of 1.2 cubic meters per hour was 

assumed (ICRP 68). The derived inhalation and ingestion intake rates based on 10% of 

Th-232 DAC are shown in the following table. 

Timeframe

Inhalation Rate 

(dpm/yr)

Ingestion Rate 

(dpm/yr)

1990-1994 266.4 5.55

 dpm = disintegrations per minute

Attachment D provides the detailed calculations used to derive these intake rates.

Ingestion doses are assigned as described in DCAS Technical Information Bulletin, 

Estimation of Ingestion Intakes, OCAS-TIB009, where the amount of activity ingested on a 

daily basis can be approximated assuming it to be 0.2 times the activity per cubic meter of 

air (SRDB Ref ID: 22397). 

1995 and forward 

Fernald’s HIS-20 database was implemented at the site in the mid-1990s, and is the 

source of BZ air monitoring data. Some of the data in HIS-20 were migrated from legacy 

health and safety databases. DOE has also provided data extracted from HIS-20 to 

NIOSH in the form of Microsoft Access tables. Thorium BZ results begin in 1993 in the 

HIS-20 database. Beginning in 1995 and later (HIS-20 database), BZ air monitoring data 

are consistently available. For thorium, the BZ results are isotopic for thorium-228, 

thorium-230 and thorium-232, although there are few thorium-228 results and these were 

always analyzed in conjunction with thorium-232. In addition to isotopic thorium results in 

HIS-20, a review conducted in August 2013 indicated five “custom” nuclides identified as: 

BL-13, BL-65, CELL 8, KS-65 and RT-210. 

Fernald used these “custom” nuclides for known mixtures of nuclides by calculating an 

effective DAC (EDAC) for the mixture to assign a more accurate DAC-Hr exposure total for 

BZ air monitoring. The likely definitions for BL-13, BL-65, and KS-65 have been located. 

These and potential definitions for CELL-8 and RT-210 are described in Attachment E, 

Interim Technical Basis for Assigning Doses from Effective DAC (EDAC) BZ Results. This 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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attachment also provides a method of calculating intakes from the EDAC data for dose 

reconstruction purposes.

Thorium workers will be assigned thorium doses based on BZ air sampling results. The 

BZ data will be used to reconstruct thorium intakes, as they are more sensitive than chest 

counts. If there are no BZ or chest count results after 1995, then no thorium doses are 

assigned. 

Chest count data and BZ air monitoring results may exist for a thorium worker in this 

timeframe. If all chest count data are negative, then only the BZ air monitoring results are 

used to evaluate thorium dose. As BZ air monitoring data are considered personal 

monitoring data and treated no different than other forms of bioassay, missed dose for BZ 

air monitoring data is included. The current ORAUT-TKBS-0017-5, (Rev 0), Technical 

Basis Document for the Fernald Environmental Management Project (FEMP) – 

Occupational Internal Dose provides a range of Minimum Detection Levels (MDLs) in 

Table 5-18. The upper value is used to assess missed dose. Reported values <MDL are 

set equal to the MDL (corrected for any respiratory protection, to be consistent with the 

reported measured results). Results are summed and assessed as an annual chronic 

intake rather than being assessed individually. The solubility class (absorption type) that is 

in the claimant’s records for each radionuclide and year is used for converting reported 

DAC-hr to activity. The “Max” option (most claimant favorable solubility type) is then 

selected for material type when entering the results into the Chronic Annual Dose (CAD) 

workbook.

When evaluating the BZ results, the DAC hours “with respirator” column are used (there 

are no totals in the “without resp” column). The DAC-hrs for each radionuclide/class 

combination are summed for each year before inputting the DAC-hr values into the DAC-hr 

conversion workbook.

However, if thorium BZ air monitoring data are negative, but there are positive chest count 

results, then chest counts likely would be used to calculate exposures to thorium. In 

instances when this occurs, an evaluation of the previous in vivo counts is performed to 

determine if the in vivo results reflect a lung burden that had been previously identified 

from earlier exposure. If the positive in vivo results are not from an earlier exposure, then 

they will be used in place of the negative BZA results to evaluate dose. 

Additionally, if there are no BZ air monitoring data, but chest counts exist (i.e. from 1979 -

1995), missed thorium dose is calculated based on chest count measurements. This is 

due to the short-term projects by a few workers where thorium handling due to 

repackaging deteriorating containers occurred. Unless there is a way to identify when the 

repackaging efforts occurred and who was involved in them, a missed dose based on 

chest counts will be done. 

Thoron Exposure
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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Thoron was present at Fernald and a portion released during the processing and storage 

of the metric tons of a variety of forms of thorium. The primary dose from thoron is to the 

respiratory tract organs and is delivered primarily by the short-lived daughter products

(SRDB Ref ID: 126391). The Thoron Exposure paper, Attachment F, provides a basis for 

recommendations of assigning thoron exposure at Fernald and includes supporting 

documentation. The table below is taken from Table F-6 of Attachment F. 

Thoron Exposure Recommendations

Time 

Period* Area/Plant WLM/year

1977 - 1979 Pilot Plant 0.03

1972 -1989 Storage facilities, repackaging, 

etc.

1.6

1972 - 2006 Closure Various Storage 0.5

WLM = Working Level Month

*Note that because thoron exposures are associated with thorium exposures, they are 

not assigned during the thorium SEC periods, (1954-1967 and 1968-1978). 

The dates and bounding levels of calculated potential exposures represent recorded 

operational history. However, thorium was present on site for most of its history. For 

unknown work locations and time periods of concern, Dose Reconstructors should assume 

that thoron exposure potential existed, as a claimant favorable assumption, and assign 

thoron doses based on the guidance from the table. Assumptions based on work history 

related to the time periods and “operational” assignments can be made to provide 

bounding assessments.

Example Dose Reconstructions

Attachment G provides example dose reconstructions performed on 4 cancers under 

multiple scenarios to demonstrate direct application of the methods presented in this 

paper. The cancers selected for the purposes of illustration were the lung, bone, prostate 

and skin. 

Conclusion

This white paper provides a methodology for the assignment of thorium and thoron doses 

at Fernald during the post SEC period, 1979 - 2006. The assessments presented in this 

white paper define the methods by which a dose estimate can be determined for Fernald 

thorium and thoron workers. These methods support NIOSH’s conclusion that the 

operationally-related internal thorium and thoron dose can be bounded. 

References
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

distribution.

 Page 20 of 146

ORAUT (Oak Ridge Associated Universities Team), 2014, Guiding Reconstruction of 

Intakes of Thorium Resulting from Nuclear Weapons Programs, ORAUT-OTIB-0076 Rev 

00-A, Oak Ridge, Tennessee, DRAFT.

Attachments

A. Post production Thorium Activities Timeline by Gene Potter

B. Methods for estimating intakes for thorium from chest counts are given in the 

supporting papers authored by Tom LaBone. 

1. Evaluation of Fernald Ac-228/Pb-212 Chest Count Data, 04/18/2013, 

2. Activity Ratios for various types of Thorium, 06/21/2013,

3. Approximate Evaluation of Pb-212 Chests Counts Following Intakes of Thorium, 

07/19/2013,

4. Using Ac-228 and Pb-212 to Measure Intakes of Th-232, 09/18/2013.

C. Thorium In Vivo Coworker (in development). 

D. Calculation for assigning thorium inhalation and ingestion doses based on 10% of a 

Th-232 DAC by Karen Kent. 

E. A Technical Basis for Assigning Doses from Effective Derived Air Concentration 

(EDAC) Breathing Zone Air (BZA) Sampling Results by Gene Potter. 

F. Thoron Exposure Paper by Bryce Rich. 

G. Fernald Example Dose Reconstructions by Karen Kent. 

ATTACHMENT A

FEMP Post-Production Thorium Activities

Year Description References

1979 Thorium processing ended.
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 21 of 146

1985 “On March 2, 1985, six breathing zone air samples were collected 

on three Plant 1 employees, who were transferring thorium 

residues from corroded drums into new drums. During this 

operation north of Building 65, all employees wore air-purifying 

half-mask respirators equipped with purple radionuclide filter 

cartridges.” (p. 2). Contains the six results that are in the “Fernald 

Thorium Air Final” database and the “AIRSAMP_thorium” 

workbook.

34321

July 15, 1985 Letter from NLO to DOE. “Over 2,000 tons of thorium 

compounds, containing approximately 1,100 tons of elemental 

thorium, are presently stored at the FMPC. Most of this material is 

stored in steel 55-gallon drums, some of which have begun to 

show serious deterioration due to corrosion ... It is necessary that 

these thorium compounds be repackaged without much delay. If 

repackaging is not done soon, some of the drums may collapse 

and spill their contents onto the floor of the warehouse where they 

are stored. That spillage would result in a serious health hazard” (p. 

2).

88205

1986 When WMCO took over the contract in January 1986, it 

“aggressively” upgraded the air sampling program, provided written 

procedures, and planned to introduce breathing zone sampling for 

all non-routine functions.

4152

Report of a task force “assembled to investigate possible 

overstressed conditions in the silo and bins used to store thorium 

oxide in Plant 8. This investigation was initiated based on a May 9, 

1986 report by Lockwood Greene which stated that overstressed 

conditions and possible failure could occur during a seismic event 

or high winds” (p. 7). Considers the options for dealing with the 

problem.

28862

Shows completed actions on Plant 8 Silo Structural Remediation 

June 1986-September 1986 (p. 7).

29071

1987 An environmental assessment identified 212 drums containing 241 

smaller containers on thorium materials stored outside of Building 

65 and more than 13,000 containers presently stored in FMPC 

warehouse buildings #64, 65, 67, and 68. An estimated 175 metric 

tons of thorium material was in the Plant 8 bin and silo storage; it 

was estimated that approximately 2,500 205-liter drums or 400 

double-walled boxes would be generated during removal of this 

material.

4611

Results of surveys taken in the thorium warehouse buildings, 64, 

65, 67, and 68 in October (p. 11).

Building Average Airborne 

Reading

Maximum Airborne 

Reading

64 0.00270 W.L. 0.00541 W.L.

65 0.41700 W.L. 0.74300 W.L.

67 0.01550 W.L. 0.02700 W.L.

68 0.65000 W.L. 0.75000 W.L.

44271
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 22 of 146

From a thorium handling environmental assessment for removal of 

the material from the Plant 8 silo and bins (aka Project 1): 

“Exposure to airborne and surface contamination will be minimized 

by personal protective equipment (PPE), routine monitoring, and 

operational procedures. Personnel exposure will be controlled to 

levels which meet DOE requirements or ALARA objectives. ... Air 

samples will be collected during repackaging operations to 

document that personnel exposures are acceptable. Airborne 

thorium concentrations within working area will not be allowed to 

exceed 0.02 becquerels alpha activity per cubic meter averaged 

over a 40-hour work week (WMCO, 1986), the Derived Air 

Concentration for Th-232 (ICRP, 1979b).” (p. 22). This is the Class 

W DAC for Th-232. One of the references in the assessment was 

the draft DOE order that became 5480.11. This seems to indicate 

that the DACs were in use even before DOE 5480.11 

implementation.

29077

26093 is 

another 

version

1988 FMPC Facility Profile June 17, 1988 indicated major environmental 

problems areas included “20,672 drum equivalents of thorium 

stored on site” (p. 5).

40307

In 1988, Fernald initiated a “three Project plan” for improving the 

temporary storage conditions for thorium (p. 203; see also Ref ID 

84457).

3559

The first project work was subcontracted to IT Corp. 33877

“The first project addresses the bulk thorium materials in the Plant 

8 silo and bins. In September 1987, the FMPC began the design 

and construction of the handling system necessary to remove and 

package the bulk thorium materials. Following construction, the 

removing, handling, and packaging of thorium began in November 

1988.” (p. 451)

3554

1989 Implementation of DOE Order 5480.11 on 1/1/1989. “The 

requirements of the revised Order are, in many cases, new or more 

stringent than those previously established. It is recognized that 

the contractor may not be in full compliance with all the 

requirements of DOE 5480.11 as of the effective date” (p. 5). The 

sites were required to submit a status report to DOE by January 27, 

1989 with requests for exemptions and an implementation plan 

detailing how compliance will be achieved by December 31, 1989 

(i.e., full compliance was not required until December 31, 1989 

unless the implementation plan specified an earlier date). There

are implementation plans for several other sites listed in the SRDB. 

This Order superseded DOE 5480.1A, Environmental Protection, 

Safety, and Health Protection Program for DOE Operations, of 8-

13-81, Chapter XI, “Requirements for Radiation Protection” (p. 10).

The DACs for Th-232 in 5480.11 were the same as those listed in 

10CFR835 final rule, namely 5E-13 μCi/ml Class W and 1E-12 

μCi/ml Class Y (p. 63)

108238, pp. 

5-82

“Prior to February 1989, no isotopic analysis for plutonium, 33900
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1979-2006 (Rev. 2) June 23, 2014

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 Page 23 of 146

neptunium, or thorium isotopes had been performed for smears or 

air sampling filters” (p. 7).

Discussion in the review of an incident in February 1989 during 

Project 1: “High volume and BZ (breathing zone) air sampling has 

been extensively performed. Instances where long lived airborne 

radioactivity was found above the 1.5 x 10-12 μCi/ml or 1 working 

level were examined as to the adequacy of respiratory protection 

provided during those periods. Respiratory protection prescribed 

for various operations consists of full face respirator for thorium 

repackaging and airline respirator for thorium storage 

containments. A full face respirator is required for work in any area 

having removable alpha surface contamination above 500 dpm/I00

cm2 until air sampling shows no significant airborne radioactivity. 

The review showed that for each instance where elevated airborne 

levels were measured, the protection factor provided by the 

prescribed respirator was adequate for personnel protection” (p. 6).

33877

Project 1 completion: “As the bulk materials were removed from 

the silo and bins, they were placed in double containment drums 

called overpacks (a 48-gallon drum is packaged inside a 55-gallon 

drum), inventoried and monitored. The drums were then stored in 

a new onsite warehouse. This project was completed in March 

1989. The silo and bins are to be decontaminated and 

demolished.” (p. 451)

3554

Training for Project 2 was not conducted until August-December 

1989.

44282

FSAR for Project 2 published in September 1989. The document 

contains a complete description of anticipated operations and 

protective measures to be employed. Airline respirators were to be 

worn by the overpacking operator and laborer, and HEPA filtered 

ventilation system was provided for the forktruck driver (p. 18). 

Access to the building was restricted during overpacking 

operations. One operator was to wear a BZ sampler outside of the 

protective clothing and a BZ sampler was to be in the forktruck. At 

least one radiation technician and health physicist were required to 

be on-site during overpacking. (p. 57-58)

4188

Thorium repackaging project air sample counting procedure, 

November 1989: “The minimum activity which the system is 

required to detect (MDA) is the 10% DAC standard, though we feel 

that the system will detect less activity.”

33954

SOP issued December (applicable to Project 2): “At least one 

operator involved in repacking shall wear a breathing zone lapel 

sampling monitor. Other personnel may be requested to wear 

monitoring equipment during the operation” (6.22). “Any 

circumstance which could result in an intake of radioactive 

materials by inhalation, ingestion or absorption, shall immediately 

be reported to a supervisor. The supervisor shall immediately

report the circumstance of possible radioactive materials intake to 

44281
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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 Page 24 of 146

Radiological Safety and or Dosimetry for evaluation. Radiological 

Safety in conjunction with Dosimetry will decide upon the 

appropriate course of action for evaluating the potential intake. 

NOTE: Operators, Radiological Safety Technicians (RST) and 

Material Control and Accountability (MC&A) personnel shall submit 

a background fecal sample prior to starting operations” (6.37)

1989 environmental report says “all thorium stored outside in 

drums is now stored indoors.” (p. 23). However, this does not 

appear to have happened until May 1990 (see below).

3555

1990 Thorium inventory dated January (start of Project 2): 15,000 drums 

stored in warehouses. 212 drums stored on an outside pad. 

Outside storage tank contained 19,585 lbs of thorium solution. (p. 

2)

83668

From a summary of radiological controls used in the thorium 

repackaging project in February (Project 2). Among the “health 

physics controls” was “Each thorium operator is required to wear a 

Breathing Zone (BZ) sampler at all times while he is inside the 

Radiological barrier fence.” (p. 3)

33882

From an SOP in March that would have applied to project 2 and 

later: “Before, at three month intervals during and at completion of 

the job, individuals working with thorium shall have in vivo lung 

measurements performed. Individuals whose work includes routine 

handling of thorium shall be required to submit background fecal 

samples prior to initiating work.” (6.3.1). “Air sample results 

indicating a thorium inhalation in excess of 8 DAC hours (with the 

respiratory protection factor considered) shall trigger in vivo 

measurement and/or bioassay.” (6.3.2). “At least one operator 

involved in the repackaging of the thorium shall be required to wear 

a BZ sampler.” (6.5.4). “Radon-220 working level samples shall be 

taken at least twice per shift” (6.5.5)

33913

Environmental Restoration and Waste Management monthly 

progress report for May: Actual work on Project 2 was January-May 

1990. “Thorium Overpacking. One hundred seventy-five drums of 

thorium had been overpacked as of April 30, 1990. Temperature 

restrictions and equipment malfunctions have hampered progress. 

Completion of Thorium Overpacking is expected in early May 

1990.” (p. 14)

33893

Press release in May: ''The second of two projects to alleviate 

environmental and safety concerns stemming from the storage of 

thorium materials at the U, S. Department of Energy's Feed 

Materials Production Center has been successfully completed.” (p. 

2)

44304

Change to OSR in May: “The proposed change would be to 

remove the pressure relief valves from the 85-gallon drum lids used 

to maintain Argon gas at 2 psi. in drums used for long term storage 

of materials designated suspect pyrophoric. These relief valves 

would be replaced with equivalent rupture discs.”

44303
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

represents preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been 

reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 25 of 146

Internal Dosimetry Technical Basis Manual, issued in December, 

“Thorium is stored on-site in approximately 15,000 containers of 

various sizes ... There are no routine ongoing operations that 

involve the processing or handling of thorium. The major potential 

source of exposure to thorium material at the FMPC is the 

repackaging of thorium drums. This operation is covered under the 

IRS&T Safety Procedure, SP-P-35-014, ‘Radiological Controls for 

Repackaging Thorium'“ (p. 47). “All compounds of thorium at the 

FMPC are assigned to inhalation class Y” (p. 48).

4145

1991 In Vitro Bioassay Requirements for the WMCO Feed Materials 

Production Center, April: Operational monitoring requirement 

specific to overpack project: “For the Thorium overpack project, 

isotopic fecal sampling is the only method capable of monitoring 

intakes below the Annual Limit on Intake. It is anticipated that 

about 50 fecal samples will be obtained for this project over the 

next year. These samples will require alpha spectrometric analysis 

for Th-232, Th-230 and Th-228 with a detection limit of 1.0 

dpm/sample.”

34636

Annual Environmental Report for 1991 covers the start of Project 3: 

1991-end of 1993 (planned), “overpacking 13,000 containers of 

thorium, was begun in 1991. Overpacking in the Thorium 

Warehouse was completed; overpacking in the Plant 1 Thorium 

Warehouse and the Pilot Plant Warehouse are scheduled for 

completion by September 1992. The FEMP has proposed to 

complete the overpacking in the (Old) Plant 5 Warehouse by the 

end of 1993.” (p. 203)

“In June 1991, approximately 1,094 metric tons (1,190 tons) of 

thorium were declared waste. Once this affirmation occurs, the 

FEMP prepares to move the thorium offsite. In September 1991, 

nearly 150 metric tons (160 tons) were sold to a commercial 

vendor. ... The majority of the thorium materials, about 13,300 

containers (containers vary in size from 55-gallon drums to drums 

as small as one gallon), is stored in the Thorium Warehouse, the 

(Old) Plant 5 Warehouse, the Plant 1 Thorium Warehouse, and the 

Pilot Plant Warehouse (Figure 53). About 9 metric tons (9.9 tons) 

of thorium nitrate solution are stored in Pilot Plant Tank 2. The 

remaining thorium material consists of about 175 metric tons (190 

tons) of bulk thorium oxide, plus inert materials like an absorptive, 

silica-rich deposit which had been contained in the Plant 8 silo and 

bins prior to their dismantling in 1989. This material is now safely 

packaged in new, double containers and is stored in Building 60.” 

(pp. 202-203)

“On July 28, 1991, the FEMP completed the overpacking of and 

relocation of 35 thorium containers characterized as mixed waste 

to a RCRA warehouse. Also completed were the necessary 

overpacking, relocation, and RCRA evaluation actions for all but 16 

of 192 containers which require further characterization ... The 

3559
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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 Page 26 of 146

characterization of the 16 remaining containers is scheduled to be 

complete in June 1992.” (p. 90-91)

1992 “During 1992, ... for the first time, the site shipped thorium wastes 

to NTS. The Fernald site continued work on the final stage of a 

three-project plan to improve the temporary storage conditions for 

the onsite thorium inventory” (p. 18). “Between January 1, 1992, 

and April 1, 1993, more than 1,600 drums of thorium materials 

were shipped to NTS. The characterization of the last 16 containers 

required to be further characterized in accordance with the SACD 

was completed in June 1992” (p. 79). “As part of the third project, 

overpacking in the Pilot Plant Warehouse was completed in 1992. 

Site personnel also conducted overpacking activities in the Plant 1 

Thorium Warehouse, and these activities are expected to be 

completed in 1993. Overpacking activities are not yet complete in 

the (Old) Plant 5 Warehouse. Until the Fernald site can provide 

final disposition of the thorium waste, safe storage will be required. 

During 1992, some of the thorium was repackaged and transferred 

to the (Old) Plant 5 Warehouse” (pp. 178).

3563

1993 “In 1993, three drums of thorium materials were shipped to the 

Nevada Test Site. Also in 1993, the site completed the 

overpacking of 6,100 drums of thorium materials and expects to 

have approval to ship those materials to Nevada in 1994” (p. 81).

3569

1994 “In 1994, the Fernald site shipped 750.4 drum equivalents of 

thorium material to the DOE Nevada Test Site (NTS) for disposal. 

Additional shipments are planned for 1995” (p. 91).

3575

1995 Building 65 Thorium Overpack Project (TOP) Project to overpack 

5,600 drums into White Metal Boxes or Thorium Overpack 

Containers and stage for shipment to NTS was anticipated to begin 

in November 1995, but did not start until 1996 (see below).

130104

“Almost 6,000 gallons of thorium nitrate, a contaminated acid waste 

stream, were treated and solidified safely in 1995 ... The final rinse 

of the thorium nitrate tank was completed November 9, 1995, less 

than two months after Chem-Nuclear, FERMCO's subcontractor, 

began processing the material.” (p. 41). In 1995, the Fernald site 

shipped 776 drum equivalents of thorium material to the NTS for 

disposal. Additional shipments are planned for 1996 (p. 104).

3578

1996 Start of TOP, May 1996 (p. 26). “Safe shutdown activities in the 

Plant 9/Thorium Complex have been completed” (p. 90). “In 1996, 

the FEMP shipped 2,112 drum equivalents or 46,101 cubic feet of 

thorium material to the DOE (NTS) for disposal” (p. 93).

3586

1997 “In 1997, the FEMP removed 3,400 containers of thorium material 

and shipped 10,875 drum equivalents, or 80,480 cubic feet (2,279 

m3

), of thorium material to the Nevada Test Site for disposal, 

completing the Thorium Overpack Project. Characterization of the 

remaining estimated 8,500 containers of thorium legacy waste at 

the FEMP was initiated in 1997” (p. 54).

3592

1998 The characterization documentation and formal RCRA waste 3604
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1979-2006 (Rev. 2) June 23, 2014

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discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not 

final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 27 of 146

determinations for the remaining estimated 8,500 containers of 

thorium legacy waste continued in 1998” (p. 51).

1999 “Thorium/Plant 9 Complex decontamination and dismantlement 

was completed. The subcontractor completed field work in 

February, including structural steel size reduction, 

decontamination, and demobilization. The project closeout report 

was submitted to the regulatory agencies and approved in April” (p. 

47). The characterization documentation and formal RCRA waste 

determinations for the remaining estimated 8,500 containers of 

thorium legacy waste continued in 1999” (p. 52).

3606

“The characterization documentation and formal RCRA waste 

determinations for the remaining estimated 8,500 containers of 

thorium legacy waste resumed in 1999” (p. 47).

129791

2000 The characterization documentation and formal RCRA waste 

determinations for the remaining estimated 8,500 containers of 

thorium legacy waste continued in 1999. In 2000 over 6,000 of 

these containers were shipped to Nevada Test Site for disposal” (p. 

47).

9010

2001 The characterization documentation and formal RCRA waste 

determinations for the remaining estimated 8,500 containers of 

thorium legacy waste were continued in 1999. Through the end of 

2001, over 6,400 of these containers were shipped to Nevada Test 

Site for disposal. This shipping effort removed over 1,000,000 

pounds (454,000 kg) of thorium from the total site thorium 

inventory” (p. 44).

3516

2002 The characterization documentation and formal RCRA waste 

determinations for the remaining estimated 8,500 containers of 

thorium legacy waste resumed continued in 1999. Through the 

end of 2002, over 7,100 of these containers were shipped to 

Nevada Test Site for disposal. This shipping effort removed over 

1,250,000 pounds (568,000 kg) of thorium from the total site 

thorium inventory” (p. 51).

126955

2003 “Through the end of 2003, over 8,400 of these containers were 

shipped off-site for treatment, with subsequent disposal at the 

Nevada Test Site. Those containers sent off-site for treatment and 

subsequent disposal included all RCRA hazardous thorium legacywaste that had a scheduled milestone of December 5, 2003. This 

shipping effort removed approximately 1,500,000 pounds (681,000 

kg) of thorium from the total site thorium inventory. The remaining 

thorium inventory of approximately 100 containers has been

evaluated. Of this remaining inventory, approximately 90 

containers are non-RCRA, low-level radioactive waste and 10 are 

RCRA hazardous waste” (p. 51).

126956

2004 The thorium waste determined to be hazardous under RCRA and 

requiring off-site treatment will be prepared and shipped by 

September 30, 2004 for treatment to meet land disposal 

restrictions. The RCRA hazardous thorium inventory amenable to 

126956
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1979-2006 (Rev. 2) June 23, 2014

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 Page 28 of 146

treatment on-site will be dispositioned by June 30, 2004” (p. 51).

“In 2004, the FCP shipped 4,274 pounds (1,940 kg) of mixed 

thorium waste to Envirocare of Utah, Inc. for treatment and 

disposal, and 21,192 pounds (9,621 kg) of non-hazardous thorium 

waste to the Nevada Test Site for disposal. At the end of 2004, 

there were only a few containers of thorium waste remaining on 

site” (p. 45).

129790

2005 “In 2005, the FCP shipped 1,051 pounds (477 kg) of mixed 

thorium-contaminated oil to Envirocare of Utah, Inc. for treatment 

and disposal. At the end of2005, there were only three containers 

of thorium-contaminated mixed waste remaining on-site. These 

containers are planned for shipment to Envirocare of Utah, Inc. in 

early 2006” (p. 48).

129791

2006 “With the completion of remediation, DOE also completed the 

disposition of the containerized waste inventory. The last shipment 

of hazardous waste occurred October 2, 2006, ending hazardous 

waste management activities” (p. 57).

10/29/2006 – remediation was complete (p. 20).

“The DOE’s Office of Legacy Management and their Technical 

Assistance Contractor, S.M. Stoller Corporation, assumed full 

responsibility for operations at the Fernald site on November 17, 

2006” (p. 15).

129793

ATTACHMENT B-1 

Evaluation of Fernald Ac-228/Pb-212 Chest Count Data

Tom LaBone 

April 18, 2013

Summary

In a previous white paper we presented a method for estimating Th-232/Th-228 intakes 

using Pb-212 chest count results. SC&A was in general agreement with this method but

expressed concerns about the relative amounts of Ac-228 and Pb-212 measured in some 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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final NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document 

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reviewed to identify and redact any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for 

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 Page 29 of 146

chest counts. Here, we show that after adjusting for bias in the chest counts the amounts 

of Ac-228 and Pb-212 present are usually consistent with the model we are using to 

evaluate the data. In the rare occasions when the amounts of Ac-228 present are 

inconsistent with this model, we recommend that the excess Ac-228 be interpreted as 

being the result of intakes of unsupported Ra-228.

Introduction

The white paper Calculation of Chronic Intake IRFs for Th-232 Assuming Shared Kinetics1

discusses how measured Pb-212 chest burdens will be interpreted in terms of Th-232/Th228 intakes. The interpretation of Ac-228 chest burdens was not addressed in that report 

because, unlike the Pb-212, the amount of Ac-228 present in the chest may not be closely 

related to the amount of Th-232/Th-228 present. This is because the Ra-228 parent of Ac228 can exist in significant quantities in the workplace independent of Th-232 because of 

its relatively long half-life (as shown in the decay scheme below).

Figure B-1 Thorium-232 decay chain (from Wikipedia) 

SC&A basically agreed with this conclusion in a white paper2 issued in 2012, but raised 

additional concerns about the chest count data:

 

1 Rev. 00, issued February 17, 2012. Authored by Tom LaBone.

2 Joyce Lipsztein and Bob Barton COMPLETENESS AND ADEQUACY OF THORIUM IN-VIVO RECORDS 

(1979–1989) S. Cohen & Associates, November 2012.
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1979-2006 (Rev. 2) June 23, 2014

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For the period 1979–1988, NIOSH has proposed to use the Pb-212 results and discard 

the Ac-228 results, as the Pb-212 results are considered more reliable. SC&A agrees 

that this is a correct statement, because the equilibrium status (relative proportion of Th232 to Ac-228 and Pb-212) of the source is not known. On the other hand, most of the 

results above the MDA have higher activity results for Ac-228 than for Pb-212. Many 

times, Ac-228 results were higher than the MDA, but Pb-212 results were below the 

MDA. NIOSH has not provided an explanation for this phenomenon.

In this report the Ac-228/Pb-212 ratios of the chest count data will be examined in an effort 

to address these concerns.

Manipulation of Fernald Chest Count Data

The Ac-228 and Pb-212 results from chest counts performed at Fernald from 1978 to 1988 

were analyzed separately by year. Based on previous experience, the distributional model 

for these annual data is that they are a combination of a normal analytical background 

distribution with a mean of zero and a lognormal exposure distribution [see RPRT-44]. The 

normal component of the data is estimated by fitting a line through the negative data on a 

normal probability plot. The intercept of the line is the estimate of the mean/median of the 

normal distribution and the slope is the estimate of the standard deviation. If the median of 

the distribution is not equal to zero the data are assumed to be biased. For example, the 

normal probability plot for the Pb-212 chest count data from 1978 are shown below in 

Figure B-1. The median of the data is -0.019 nCi, which means that the data are assumed 

to be biased by that much. The data are adjusted for any bias and then refit in order to 

force the line through zero (i.e., make the median equal to zero). For example, the 

adjusted 1978 Pb-212 data are shown below in Figure B- 2.

Figure B-2 Normal probability plot of Pb-212 chest count results for 1978. The line 

is a robust regression of the data that are less than zero nCi.

-3 -2 -1 0 1 2 3

-0.5 0.0 0.5 1.0

Standard Normal Quantiles

Pb-212 (nCi)

Bias = -0.019 nCi
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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Figure B-3. Normal probability plot of Pb-212 chest count results for 1978 after 

adjusting for bias. The line is a robust regression of the data that are less than zero 

nCi.

The process decision level (DL) above which a measured chest burden is deemed to be 

"positive" is taken to be the 95th percentile of the (unbiased) normally distributed analytical 

background. For the 1978 Pb-212 data, the DL is 0.12 nCi as shown in Figure B-3. 

Measured Pb-212 chest burdens below this DL are deemed to not indicate the presence of 

Pb-212.

Figure B-4. Normal probability plot of Pb-212 chest count results for 1978 after 

adjusting for bias. The line is a robust regression of the data that are less than zero 

nCi, and the red point is the 95th percentile of the background normal distribution 

(i.e., the decision level).

A summary of the bias and DL for Ac-228 and Pb-212 for years 1978 through 1988 are 

given in Table B-1 below and the corresponding plots are given in Appendix A. The DL's 

for Pb-212 ranged from 0.11 to 0.18 with a mean of 0.13 whereas the DL's for Ac-228 

-3 -2 -1 0 1 2 3

-0.5 0.0 0.5 1.0

Standard Normal Quantiles

Pb-212 (nCi)

Bias = 0 nCi

-3 -2 -1 0 1 2 3

-0.5 0.0 0.5 1.0

Standard Normal Quantiles

Pb-212 (nCi)

DL = 0.12 nCi
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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ranged from 0.08 to 0.17 with a mean of 0.11. For simplicity, a single DL of 0.12 nCi will be 

adopted for both nuclides for all years. If a minimum detectable amount (MDA) is need for 

dose reconstruction purposes, a value of 2DL = 0.24 nCi should be used for both 

nuclides.

Table B-1. Summary of bias and DL for Ac-228 and Pb-212 for each year.

Pb-212 Pb-212 Ac-228 Ac-228

Year Bias (nCi) DL (nCi) Bias (nCi) DL (nCi)

1978 -0.019 0.120 0.008 0.153

1979 -0.014 0.156 0.031 0.169

1980 -0.045 0.123 0.025 0.091

1981 -0.056 0.108 0.022 0.127

1982 -0.058 0.121 0.010 0.117

1983 -0.101 0.122 -0.008 0.097

1984 -0.089 0.111 0.001 0.079

1985 -0.086 0.117 0.017 0.102

1986 -0.085 0.128 0.020 0.114

1987 -0.047 0.123 0.008 0.106

1988 0.002 0.181 0.058 0.107

Discussion of Ac-228 and Pb-212 in Chest Counts

In Figure B-4, chest burdens from 1978, where both Ac-228 and Pb-212 are greater than 

the DL, are presented (Ac-228/Pb-212 plots for all years are presented in Appendix B). 

These data are considered to be above the level of analytical noise and represent actual 

material in the chest3

. The diagonal blue line has a slope of 1 and an intercept of 0. Data 

falling exactly on this line have equal quantities of Ac-228 and Pb-212. All of these 

measurement, except for one, are considered to indicate equal quantities of Ac-228 and 

Pb-212 in the chest (to within measurement uncertainty).

 

3 If one looks at the Ac-228 to Pb-212 ratio and includes results that are basically noise, one can expect to see 

quite a range of ratios beyond the anticipated 1:1 that will be very difficult to interpret in a meaningful way.
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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Figure B-5. Plot of Ac-228 versus Pb-212 for 1978 where the levels of both nuclides 

are above the decision level. The blue line has a slope of 1 and an intercept of 0.

The lone outlier has an Ac-228/Pb-212 ratio of ~18. The only plausible explanation for 

such a large ratio is the presence of unsupported Ra-228. This suggests that the Ac-228 

activity in excess of the Pb-212 activity should be interpreted as a Ra-228 intake and 

assessed separately from the Th-232/Th-228 intake estimated from the Pb-212. Acute and 

chronic intakes of Ra-228 measured with Ac-228 are readily evaluated with IMBA and do 

not require custom treatment. 

Appendix A

Two plots are given for each year. The first is a normal probability plot of the Pb-212

data. The median of the Pb-212 data was estimated from a robust regression to the

negative (less than zero) data. The median, which is identified as the "bias" on the plot,

was then subtracted from each result. The data on the plot are bias-corrected. The

regression was repeated on the bias-corrected data to obtain the standard deviation and

mean of the normal background distribution. These parameters were then used to

calculate the decision level (DL), which is assigned the 95th percentile of the normal

background data. The second plot is the same as the first except it is for Ac-228.

Appendix B

For each year four plots of Ac-228 versus Pb-212 are given:

The first plot is the Ac-228 versus the Pb-212 where both nuclides are above the DL.

The second plot is the same data as the first plot but with a different scale on the X and Y 

axes.

The third plot is the Ac-228 versus the Pb-212 where either nuclide is above the DL.

-1 0 1 2 3 4 5

-1

0 1 2

3

4

5

 

Pb212

Ac228
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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The fourth plot is the same data as the first plot but with a different scale on the X and Y 

axes.

1978 (Ac and Pb Results > 0.12 nCi)
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White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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1979-2006 (Rev. 2) June 23, 2014

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1979-2006 (Rev. 2) June 23, 2014

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White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 

1979-2006 (Rev. 2) June 23, 2014

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1979-2006 (Rev. 2) June 23, 2014

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1979-2006 (Rev. 2) June 23, 2014

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ATTACHMENT B-2 

Activity Ratios for Various Types of Thorium

Tom LaBone 

June 21, 2013

In an April 18, 2013 white paper entitled Evaluation of Fernald Ac-228/Pb-212 Chest Count 

Data I recommended that chest counts with a high Ac-228 : Pb-212 ratio (greater than 1.5 

: 1) be interpreted as intakes of a mixture of triple-separated thorium and unsupported Ra228. During the Fernald working group call on June 17, it was suggested that we should 

instead interpret these chest counts as being the result of intakes of some form of freshly 

separated thorium. I have looked at this issue for a while now and I am unable to identify a 

form of separated thorium likely to be encountered at Fernald that would explain the 

observed high Ac-228 : Pb-212 ratios. The following discussion documents my 

calculations.

The decay scheme of Th-232 down to Pb-212 is shown below:

10 232 1.405 10 228 5.75 6.13 228

228 1.91 224 3.62 220 55.6 2 0.146 10.6

228

16 2 21

yyh

yd s sh

Th Ra Th

Th Ra Rn

c

P

A

o Pb

→ → → ×

→ → → → →

The radionuclides of interest, i.e., those that can be quantified with a chest count, are the 

Ac-228 and the Pb-212. 

A chemical separation or stripping of the thorium will remove all non-thorium elements.

Immediately after separation, the daughters of Th-232 and Th-228 will start to grow in. A 

cursory examination of the half-lives of the members of this decay chain reveals that:

• A few weeks after separation, the Pb-212 present is equal to the amount of Th-228 

that is present.

• A couple of days after separation, the Ac-228 present is equal to the amount of Ra228 that is present.

It is important to note that when separations are performed the Ac-228 present is not 

necessarily related to the amount of Th-232 present because the Ra-228 has a half-life 

long enough to permit its presence in the workplace independent of its parent Th-232. On 

the other hand, if Pb-212 is observed then there must necessarily be Th-228 present, and 

if there is Th-228 present then there must be Th-232 present (although not in equal 
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quantities). This is why we chose to evaluate the Pb-212 chest count data rather than the 

Ac-228 chest count data.

We are interested in the Ac-228 : Pb-212 ratios that might be encountered in chest counts 

performed on workers following exposure to thorium in the workplace. The thorium 

mixtures4 examined here are:

• Single-Sep Thorium is Th-232 in equilibrium with all of its daughters that is then 

stripped of the non-thorium daughters. Immediately after the stripping procedure is 

completed, all that remains are Th-232 and Th-228 in a 1 : 1 activity ratio.

• Double-Sep Thorium is Single-Sep Thorium that is aged 4.55 years and then 

stripped of the non-thorium daughters. Immediately after the stripping procedure is 

completed, all that remains are Th-232 and Th-228 in a 1 : 0.422 activity ratio.

• Triple-Sep Thorium is Double-Sep Thorium that is aged 2.536 years and then 

stripped of the non-thorium daughters. Immediately after the stripping procedure is 

completed, all that remains are Th-232 and Th-228 in a 1 : 0.263 activity ratio.

• Enriched Thorium has a Th-232 : Th-228 activity ratio of 1 : 0.0006. This material is 

essentially pure Th-232 by activity and could only be produced by some sort of 

intentional enrichment process.

• Dirty Thorium is thorium that is separated from the radium with a 10 : 1 

decontamination factor. Thus, immediately after the separation procedure the Th232 : Ra-228: Th-228 : Ra-224 ratios are 1 : 0.1 : 1 : 0.1.

The first five plots show the quantity of Ac-228 and Pb-212 present in the chest following 

acute inhalation intakes of each of the five types of thorium described above, each being 5 

μm AMAD Type S aerosols. On the sixth plot the Ac-228 : Pb-212 ratio for all five 

materials are presented. These plots were constructed from intake retention fractions 

generated with DCAL, which accurately implements the independent biokinetics of the 

thorium chain.

The pink dashed line on the sixth plot shows a 20 : 1 ratio, which is a ratio that has been 

observed in an actual chest count of a worker at Fernald. This plot demonstrates that a 20 

: 1 ratio would be observed only in the cases where something exotic like Enriched 

Thorium is inhaled, or if unsupported Ra-228 is inhaled along with a more realistic form of 

thorium5

. I consider the latter explanation to be the only plausible one at Fernald.

 

4 Note that Single-Sep, Double-Sep, and Triple-Sep Thorium are defined differently than in previous technical 

papers because we are interested in the composition of the material immediately after separation.

5 The same conclusions are reached with Type M material and for whole-body counts.
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P

b-212

Chest Burden (nCi)

1e-0

4 1e-03 1e-02 1e-01

ATTACHMENT B-3 

Approximate Evaluation of Pb-212 Chests Counts Following Intakes of Thorium

Tom LaBone 

July 19, 2013

In this paper I suggest ways to adjust intakes and intake rates of Th-232 and Th-228

calculated from Pb-212 chest burdens with IMBA so that the intakes and intake 

rates will not underestimate those calculated with exact methods (DCAL). These 

adjustments may be used when an overestimate of dose is appropriate. Best 

estimates of dose require the use of DCAL.

Acute Intakes

Assume a mixture of 1 nCi of Th-232 and 1 nCi of Th-228 (both being 5 μm 

AMAD Type S material) was inhaled. The Pb-212 chest burden as a function of 

time after the acute intake is shown in Figure 1 below.

Figure 1. Pb-212 chest burden following an acute inhalation intake of Type S thorium 

having a Th-228 to Th-232 ratio of 1 : 1.

Type S Equilibrium Thorium

Approx (blue) 

Exact (red) 

1 5 10 50 100 500 5000

Time of Chest Count (days) 1 nCi Th-232 & 1 nCi Th-228

The exact chest burden q of Pb-212 at t days after an acute inhalation intake is given by

where qpbth232 is the chest burden of Pb-212 that grows in from the inhaled Th-232 and
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qpbth228 is the chest burden of Pb-212 that grows in from the inhaled Th-228. These 

exact burdens are calculated with DCAL, which accounts for independent kinetics of the 

thorium decay chain and the loss of Rn-220. Two approximations can be made here:

• The amount of Pb-212 present equals the amount of Th-228 present at all 

times after the intake, i.e.,

• There is negligible ingrowth of Pb-212 from the Th-232 component of the 

intake, i.e.,

 

This gives the following approximation to q: 

 

where qth228 is the Th-228 chest burden at time t (which can be calculated with IMBA). 

As seen in the plot above, these approximations provide reasonably accurate estimates 

of the Pb-212 burden between approximately10 and 1000 days after the intake.

For example, assume that a Pb-212 chest burden of 1.5 nCi is observed at 100 days 

after an acute inhalation intake of this Type S thorium. The intake of Th-232 is

 

 

which translates into 48.95 nCi of Th-228. These intakes can be checked by 

calculating the expected Pb-212 chest burden and seeing if it equals the burden from

which the intakes were calculated: 

 
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With the approximate method we have a Th-228 intake of

 

which translates into a 45.18 nCi intake of Th-232.

In this discussion I present plots of Pb-212 chest burdens calculated with the exact and 

approximate methods given thorium intakes. I find these plots to be intuitive and easier to 

interpret than other types of plots. Note that in this example

• for a given intake the exact method gives a lower chest burden than 

does the approximate method at t = 100 days (see the plot above), but

• for a given chest burden the exact method gives a larger intake than 

does the approximate method.

In practice we will typically calculate intakes from chest burdens. Thus, the plot in Figure

1 can be interpreted to mean that the approximate method will underestimate intakes 

at times prior to ~300 days after the intake (where the curves cross) and overestimate 

intakes after that day.

Triple Separated Thorium Mixture

Now assume a mixture of 1 nCi of Th-232 and 0.19 nCi of Th-228 (both being 5 μm 

AMAD Type S material) was inhaled. The Pb-212 chest burden as a function of time 

after the acute intake is shown in Figure 2 below. Thorium with a Th-228 : Th-232 ratio 

of 0.19 : 1 is referred to as Triple Separated Thorium. 

Figure 2. Pb-212 chest burden following an acute inhalation intake of Type S 

thorium having a Th-228 to Th-232 ratio of 0.19 : 1.
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The exact chest burden q of Pb-212 at t days after an acute inhalation intake is given by

Applying the two approximations gives the following approximation to q: 

For example, assume that a Pb-212 chest burden of 1.5 nCi is observed at 100 days 

after an acute inhalation intake of this Type S thorium. The intake of Th-232 is

which translates into (0.19)(255.96 nCi) = 48.63 nCi of Th-228. As a check, it is useful to 

show that
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With the approximate method the intake of Th-228 is

which gives (45.18 nCi) / (0.19) = 237.79 nCi of Th-232.

The plot for Type M triple separated thorium is shown below. Other than the fact that there 

is faster clearance of the thorium from the chest, all of the discussion above is directly 

applicable to Type M material.

Figure 3. Pb-212 chest burden following an acute inhalation intake of Type M 

thorium having a Th-228 to Th-232 ratio of 0.19 : 1.
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Adjustment of Thorium Intakes

As shown in the plots above, for a given thorium intake, the approximate method will 

overestimate the Pb-212 chest burden for a length of time after the intake (~2 years for 

Type S material). Thus, for a given Pb-212 chest burden, the approximate method will 

underestimate the thorium intake for the same length of time. In Figures 4 and 5, an 

adjustment factor of 1/1.1 is applied to the approximate Pb-212 chest burdens to ensure 

that they do not overestimate the exact Pb-212 chest burdens at times greater than 30 

days post intake.

Figure 4. Pb-212 chest burden following an acute inhalation intake of Type S 

thorium having a Th-228 to Th-232 ratio of 0.19 : 1. The vertical dashed line is at t = 

30 days post intake.
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Figure 5. Pb-212 chest burden following an acute inhalation intake of Type M 

thorium having a Th-228 to Th-232 ratio of 0.19 : 1. The vertical dashed line is at t = 

30 days post intake.
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When using the approximate method to calculate thorium intakes from Pb-212 chest 

burdens, the intake is multiplied by an adjustment factor of 1.1 to achieve the desired end 

of not underestimating the intake that would have been calculated using the exact

method.

Guidance for Acute Intakes

Based on discussion given above, the following guidance is offered on how to use 

the approximate method to evaluate Pb-212 chest count data following acute 

inhalation intakes of Type M or S thorium: 

Assume we have a single measured Pb-212 chest burden. Evaluate the chest burden 

with a Th-228 biokinetic model in IMBA. Multiply the calculated Th-228 intake by a 

factor of

1.1 and assign it as the intake of Th-228. Divide this estimated Th-228 intake by the Th228 : Th-232 ratio of 0.19 : 1 to obtain the Th-232 intake. For Pb-212 chest 

burdens measured more than 30 days after an acute intake, these approximate 

intakes will not underestimate the intakes calculated with exact methods.

Chronic Intakes

The plot in Figure 4 below shows the Pb-212 chest burden as a function of time 

following a chronic intake of 1 nCi/day of Th-232 and 0.19 nCi/day of Th-228 (both 

being 5 μm AMAD Type S material). In other words, the time on the abscissa is the 
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length of the time after the start of the chronic intake and the time that the chest burden

is determined. The two curves cross at ~700 days.

Figure 6. Pb-212 chest burden following a chronic inhalation intake of Type S 

thorium having a Th-228 to Th-232 ratio of 0.19 : 1.

The equations for chronic intakes are essentially the same as in the case of acute 

intakes except that the functions have an argument for the length of the constant 

chronic intake period. The exact chest burden q of Pb-212 at t days after the start of a

tc day chronic inhalation intake is given by

Applying the two approximations gives the following approximation to q: 

For example, assume that a Pb-212 chest burden of 1.5 nCi is observed at the end of a

365-day chronic inhalation intake of Type S triple separated thorium. The total intake of

Th-232 is
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which translates into (0.19)(288.1 nCi) = 54.74 nCi of Th-228. This can be seen by 

rearranging the above equation:

The intake rates are obtained by dividing the intakes by tc = 365 days. With the 

approximate method the intake of Th-228 is

which gives (50.34 nCi) / (0.19) = 264.9 nCi of Th-232. 

The plot for Type M triple separated thorium is shown in Figure 5 below. After a few 

hundred days the Pb-212 chest burden achieves a steady state condition with the 

approximate method giving a chest burden ~10% higher than the exact method.
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Figure 7. Pb-212 chest burden following a chronic inhalation intake of Type M thorium

having a Th-228 to Th-232 ratio of 0.19 : 1.

Adjustment of Chronic Thorium Intakes

In Figures 8-13, the Pb-212 chest burdens at various times during and after 365 day, 1000 

day, and 5000 day constant chronic intakes are presented. As was done with the acute 

intakes, the approximate Pb-212 chest burdens are adjusted by a factor of 1/1.1. This 

illustrates that intake rates calculated from Pb-212 chest counts with the approximate method 

can be adjusted by a factor of 1.1 to ensure that the intake rates do not underestimate the

intake rates calculated with the exact method.

Figure 8. Pb-212 chest burden during and following a 365-day chronic inhalation intake 

of Type S thorium having a Th-228 to Th-232 ratio of 0.19 : 1. The vertical dashed line is

at t = 365 days.
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Figure 9. Pb-212 chest burden during and following a 1000-day chronic inhalation intake

of Type S thorium having a Th-228 to Th-232 ratio of 0.19 : 1. The vertical dashed line is

at t = 1000 days.
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Figure 10. Pb-212 chest burden during and following a 5000-day chronic inhalation 

intake of Type S thorium having a Th-228 to Th-232 ratio of 0.19 : 1. The vertical dashed 

line is at t = 5000 days.
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Figure 11. Pb-212 chest burden during and following a 365-day chronic inhalation intake

of Type M thorium having a Th-228 to Th-232 ratio of 0.19 : 1. The vertical dashed line is at 

t = 365 days.
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Figure 12. Pb-212 chest burden during and following a 1000-day chronic inhalation

intake of Type M thorium having a Th-228 to Th-232 ratio of 0.19 : 1. The vertical dashed 

line is at t = 1000 days.
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Figure 13. Pb-212 chest burden during and following a 5000-day chronic inhalation intake 

of Type M thorium having a Th-228 to Th-232 ratio of 0.19 : 1. The vertical dashed line is at 

t = 5000 days.
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Guidance for Chronic Intakes

Based on discussion given above, the following guidance is offered on how to use the 

approximate method to evaluate Pb-212 chest count data following constant chronic 

inhalation intakes of triple separated thorium: 

Assume we have a single measured Pb-212 chest burden. Evaluate the chest burden with a 

Th-228 biokinetic model in IMBA. Multiply the calculated Th-228 intake rate by a factor of 1.1 

and assign it as the intake rate of Th-228. Divide this estimated Th-228 intake rate by the Th228 : Th-232 ratio of 0.19 : 1 to obtain the Th-232 intake rate. For chronic intakes longer than 

1 year these approximate intakes will not underestimate the intakes calculated with exact 

methods.

ATTACHMENT B-4 

Using Ac-228 and Pb-212 to Measure Intakes of Th-232
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Tom LaBone 

September 18, 2013

Introduction

The following four reports issued over the past 18 months present the technical basis for using 

Pb-212 measured chest burdens to calculate inhalation intakes of Th-232 at Fernald and at 

other facilities where thorium was chemically processed:

Calculation of Chronic Intake IRFs for Th-232 Assuming Independent Kinetics, February 17, 

2012. In this paper we present the theoretical basis for calculating intake retention fractions 

that account for independent biokinetics of the Th-232 decay chain. In other words, we 

demonstrate that we have the models and computational wherewithal to properly evaluate 

acute and chronic intakes of Th-232 and Th-228 based on Ac-228 and Pb-212 chest burden 

measurements. In addition, the default thorium referred to as "triple separated thorium" that 

will be used in dose reconstructions at Fernald is introduced in this paper.

Evaluation of Fernald Ac-228/Pb-212 Chest Count Data, April 18, 2013. In this paper we 

review Ac-228/Pb-212 chest counts from Fernald, adjust these results for bias, and develop 

decision levels for each radionuclide.

Activity Ratios for Various Types of Thorium, June 21, 2013. In this paper we explore the 

levels of Ac-228 and Pb-212 expected to be present in the chest after intakes of various 

mixtures of Th-232/Th-228.

Approximate Evaluation of Pb-212 Chest Counts Following Intakes of Thorium, July 19, 

2013. In this paper we present methods for using IMBA to make conservative estimates of 

Th-232 intakes from Pb-212 chest burden measurements, which facilitates dose 

reconstructions when an overestimate of dose is appropriate.

Taken together, the information in these four papers provides the technical basis and 

implementing procedures needed to perform a dose reconstruction for an individual with Ac-228 

and Pb-212 chest count results. 

The decay scheme of Th-232 down to Pb-212 is shown in Figure 1. The radionuclides of 

interest, i.e., those that can be quantified with a chest count, are the Ac-228 and the Pb-212. 

We chose to evaluate thorium intakes using primarily the Pb-212 chest count data rather than 

the Ac-228 chest count data. This paper summarizes the reasons for this decision, using 1980 

chest counts from Fernald to illustrate. 

Figure 1. Decay scheme of Th-232.
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Ac-228 and Pb-212 Kinetics

A chemical separation or stripping of the thorium will remove all non-thorium elements, leaving 

(more or less) only the Th-232 and Th-228. Immediately after separation, the daughters of Th232 and Th-228 will start to grow in. This process of ingrowth impacts the use of Ac-228 and 

Pb-212 for estimating the intake of the parent Th-232 in different ways. Specifically:

Ac-228

A couple of days after separation, the Ac-228 present is equal to the amount of Ra-228 

that is present. The amount of Ac-228 present is not necessarily related to the amount of 

Th-232 present because the Ra-228 has a half-life long enough to permit its presence in 

the workplace for years independent of its parent Th-232. Starting with pure Th-232, the 

amount of Ac-228 present is very sensitive to the length of time that has elapsed since 

the separation of the Th-232 from its progeny.

Pb-212 

A few weeks after separation, the Pb-212 present is equal to the amount of Th-228 that 

is present, less any Rn-220 that is lost from the body. The loss of Rn-220 from the body 

is expected to be minimal because of its short half-life, and the ICRP biokinetic model for 

inhaled Th-232 explicitly accounts for this loss. Thus, if Pb-212 is observed then there 

must necessarily be Th-228 present, and if there is Th-228 present then there must be 

Th-232 present. However, the ratio of Th-232 to Th-228 is sensitive to the number and 

timing of chemical separations that have been performed on the thorium. 

To illustrate the practical consequences of these characteristics of Ac-228 and Pb-212, both will 

be used to evaluate a chest count performed at Fernald in 1980.

Fernald Chest Counts 
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The Ac-228 and Pb-212 results for all 184 chest counts performed in 1980 at Fernald are 

plotted in Figure 2. We are interested in the counts where both Ac-228 and Pb-212 are above 

the decision level of 0.12 nCi, which are shown in Figure 3. The blue lines in these plots have a 

slope of 1 and intercept of 0, indicating the case where the Ac-228 activity equals the Pb-212 

activity. The difference between the Ac-228 activity and the blue line is of no practical 

significance, as is shown in Figure 4 where ± 30% error bars, representing typical measurement 

uncertainty, are added to the plot. 

 Figure 2. All Ac-228 and Pb-212 results for 1980 (in nCi) for 184 chest counts

 performed in 1980. The solid blue line indicates where the Ac-228 equals 

 Pb-212.

 

 

 

Figure 3. All Ac-228 and Pb-212 results (in nCi) for 27 chest counts performed in 1980 

where both counts were above the decision level of 0.12 nCi. The count indicated 
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by the solid red point has 0.64 nCi of Ac-228 and 0.51 nCi of Pb-212. The solid blue 

line indicates where the Ac-228 equals Pb-212.

 

Figure 4. Same plot as shown in Figure 2 with the addition of ±30% 

 error bars representing measurement uncertainty.

 

Intake Calculations

0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.4 0.8

 ( 

Pb212

Ac228

0.0 0.2 0.4 0.6 0.8 1.0

0.0 0.4 0.8

 

Pb212

Ac228
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The count indicated by the solid red point in Figure 3 has an Ac-228 activity of 0.64 nCi and a 

Pb-212 activity of 0.51 nCi. Acute inhalation intakes of Type S Th-232 can be calculated from 

the Ac-228 chest count by assuming that the measurement was performed at a particular time 

after intake of "pure" thorium (no Ra-228). For example, if a 0.64 nCi chest burden of Ac-228 

was measured at 50 days post intake, the estimated intake of Th-232 is 892 nCi. Note that this 

intake estimate is independent of the Th-232 to Th-228 ratio (i.e., it is independent of the 

number of separations performed on the thorium). 

Acute inhalation intakes of Type S Th-232 can also be calculated from the Pb-212 chest count 

by assuming that the measurement was performed at a particular time after intake of pure 

thorium that has a specified Th-232 to Th-228 ratio. For example, if a 0.51 nCi chest burden of 

Pb-212 was measured at 50 days post intake, the estimated intake of Th-232 is 70 nCi, 

assuming that we are dealing with triple-separated thorium (which specifies a Th-232 to Th-228 

ratio).

Repeating these calculations for chest counts performed at days 1 through 7000 following the 

acute intake creates the intake lines shown in Figure 5 (which one should note has log-log 

scales). 

 Figure 5. Intakes of triple-separated Type S Th-232 calculated from chest

 burdens of 0.64 nCi of Ac-228 (red line) and 0.51 nCi of Pb-212 (blue line) 

 as a function of time after an acute inhalation intake the chest burden was

 measured. 

 

After a year or two the Th-232 intakes estimated from the Ac-228 and Pb-212 are similar 

enough to be considered equal for all practical purposes. Prior to this time the Th-232 intakes 

10 20 50 100 200 500 1000 5000

10 50 500 5000

Time After Intake (days)

Th-232 Intake (
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estimated from the Ac-228 are significantly higher than the Th-232 intakes estimated from the 

Pb-212, reflecting the strong dependence of the Ac-228 burden on the time elapsed since 

separation. 

Assuming something other than triple-separated thorium will increase the difference, as shown 

in Figure 6 where the ratio of Th-232 to Th-228 is assumed to be 1:1 (i.e., an equilibrium 

thorium mixture).

 Figure 6. Intakes of equilibrium Type S Th-232 calculated from chest

 burdens of 0.64 nCi of Ac-228 (red line) and 0.51 nCi of Pb-212 (blue line) 

 as a function of time after an acute inhalation intake the chest burden was

 measured

 

Thus, given that we are dealing with an acute inhalation intake of triple-separated Type S 

thorium, the chest count indicating an Ac-228 activity of 0.64 nCi and a Pb-212 activity of 0.51 

nCi had to have been performed at some time much greater than 50 days post intake. Indeed, 

because thorium separation activities ceased at Fernald in 1979, a time post separation of over 

a year is most likely in this case.

In general, if a Th-232 intake calculated from a measured Ac-228 chest burden is much larger 

than the Th-232 intake calculated from a measured Pb-212 chest burden, we have either 

assumed the wrong time post separation for the chest count or there is unsupported Ra-228 

present in the inhaled material (see Evaluation of Fernald Ac-228/Pb-212 Chest Count Data). In 

either case, the Th-232 intake calculated from the Pb-212 is considered to be the more accurate 

intake estimate.

In the case of a chronic intake, there is less of a difference between intakes estimated from the 

Ac-228 and Pb-212 chest burdens. For example, if a 0.64 nCi chest burden of Ac-228 was 

measured at 50 days after the end of a 365-day chronic intake of triple-separated Type S 

10 20 50 100 200 500 1000 5000

10 50 500 5000

Time After Intake (days)

Th-232 Intake 
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thorium, the estimated intake of Th-232 is 297 nCi. If a 0.51 nCi chest burden of Pb-212 was 

measured at 50 days after the end of the chronic intake, the estimated intake of Th-232 is 110 

nCi. Repeating these calculations for chest counts performed at days 1 through 7000 after the 

end of a 365-day chronic intake creates the intake lines shown in Figure 7.

 Figure 7. Intake of triple-separated Type S Th-232 calculated from chest 

 burdens of 0.64 nCi of Ac-228 (red line) and 0.51 nCi of Pb-212 (blue line) 

 as a function of time after the end of a 365-day chronic inhalation intake.

 For example, day 20 on the x-axis is 20 days after the end of the 365-day 

 chronic intake.

Conclusion

Thorium-232 intakes can be estimated from measurements of Ac-228 or Pb-212 in the chest. 

Here and in previous white papers we have presented technical discussions that support our 

use of Pb-212 chest burdens combined with the assumption of triple-separated thorium to 

estimate Th-232 intakes. This approach is unlikely to underestimate the Th-232 intake and 

avoids the potential gross overestimates associated with the use of Ac-228.

ATTACHMENT C

10 20 50 100 200 500 1000 5000

50 100 200 500

Time After End of Chronic Intake (days

Th-232 Intake (
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In Development
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June 23, 2014 

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ATTACHMENT D

Thorium (Class W) inhalation intake rate at Fernald based on 10% of Th-232 DAC

100% Th-232 DAC 5.00E-13 μCi/cm3 

10% Th-232 DAC 5.00E-14 μCi/cm3 (5.00E-14 μCi/cm3 x 2.22 E+06 dpm/μCi) = 1.11E-07 dpm/cm3 

 (1.11 E-07 dpm/cm3 based on 2.22E+06 dpm/μCi)

Work Year 2000 hr/yr (2000 hr/yr / 8 hrs/d) = 250 days

Breathing Rate (ICRP 68) 1.2 m3

/hr (1.2E+06 cm3/hr based on 1.00 E+06 cm3m3) 

OCAS TIB-009 0.2 (Intake per workday, not calendar day = 250 days) 

Annual Inhalation Intake of Th-232 266.400 dpm/yr (1.11E-07 dpm/cm3

 x 1.2 E+06 cm3/hr x 2000 hr/yr = 266.4 dpm/yr) 

Annual Ingestion Intake of Th-232 5.550 dpm/yr (1.11E-07 dpm/cm3 x 1.00 E+06 cm3

/m3 x 0.2 x 250 d/yr = 5.55 dpm/yr)

Note: Both 10 CFR 835 and DOE 5480.11 DAC for Th-232 (Class W) is 5.00 E-13 μCi/cm3 
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ATTACHMENT E

Interim Technical Basis for Assigning Doses from Effective DAC (EDAC) BZ Results

Historically the Fernald site used the most restrictive DAC to limit exposures to airborne thorium 

and its daughter products. The standard procedure was to count the air samples in a lowbackground proportional counter. This instrument was capable of measuring total alpha activity 

(beta-gamma activity was ignored by the appropriate setting on a pulse-height discriminator). 

By 1995, it was recognized that this method, while conservative, did not provide accurate results 

(SRDB 3547). The solution was to develop an effective DAC (EDAC) for each specific mixture 

of radionuclides that would apply to specific locations and/or operations on site. The equation 

used was:

EDAC = 1

∑ fi

DACi

 (Equation 1)

Where:

fi = the activity fraction of isotope i in the airborne mixture

DACi = The DAC of isotope i” (SRDB 3560)

If the mixture in question included beta emitters, then it was necessary to adjust the EDAC 

calculated from the above equation so that the exposure in EDAC-hours was calculated 

correctly. This was done by multiplying the EDAC by the fraction of the isotopes that were 

alpha emitters. The value of the alpha-count-adjusted EDAC is not important for dose 

reconstruction.

The HIS-20 database was implemented at Fernald in the mid-1990s. Some of the data it 

contains were migrated from legacy health and safety databases. The HIS-20 database is the 

source of the DOE-provided breathing zone (BZ) data. DOE has also provided data extracted 

from HIS-20 to NIOSH in the form of Microsoft Access tables. The data in the BZ table indicate 

thorium BZ results first appear in 1993. The first EDAC, designated BL-65 (Building 65), was 

recorded in 1996. A technical basis for this EDAC had been published in 1995 (SRDB 3547). 

The four other EDACs in HIS-20 are not formally documented in any of the documents captured 

so far. This paper provides an interim method of calculating intakes from the EDAC data for 

dose reconstruction purposes.

The Table E-1 summarizes the EDAC results in the Fernald HIS-20 database which was 

provided to NIOSH.
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Table E-1, Count of Effective DAC Results in HIS-20

NUCLIDE Count of Results Min Year Max Year

BL-13 924 2003 2004

BL-65 5260 1996 2003

CELL 8 2 2005 2005

KS-65 23034 2004 2006

RT-210 489 2001 2006

The likely definitions for BL-13, BL-65, and KS-65 have been located. These and potential 

definitions for CELL-8 and RT-210 are discussed in the following sections.

BL-13

The BL-13 EDAC is documented in a memorandum from Connell to Kent and Thiel, October 13, 

2003 (SRDB 129871) and SD-1064, “Technical Basis: Air Sampling Plan for Demolition Closure 

Projects,” Rev 6, February 9, 2004 (SRDB 132933). The EDAC calculated for a mixture of Th232, Th-230, Th-228, and total uranium was 3.28E-12 μCi/ml. The author recommended that it 

be rounded down to 3.0E-12 μCi/ml to be consistent with another project. The mean activity 

fractions from SD-1064 appear in Table E-2. It should be noted that the name given to this 

EDAC in SD-1064 was “B13A.” However, there are no results in HIS-20 with this designation, 

and it was assumed that the results were entered into HIS-20 as “BL-13.” 

Table E-2, Activity Fractions for the BL-13 EDAC

Isotope/Element Activity Fraction

Th-232 0.083

Th-230 0.259

Th-228 0.098

U-total 0.560

Dose Reconstructors should multiply the reported number of BL-13 DAC-hours by 3.0E-12 

μCi/ml/DAC and the breathing rate (1.2E+06 ml/hour) to get the total intake. They then should 

multiply the total intake by the respective activity fractions for Th-232, Th-230, Th-228, and total 

uranium, as follows:

• Th-232: intake (μCi) = reported DAC-hrs × 3.0E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.083

• Th-230: intake (μCi) = reported DAC-hrs × 3.0E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.259

• Th-228: intake (μCi) = reported DAC-hrs × 3.0E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.098

• U-total: intake (μCi) = reported DAC-hrs × 3.0E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.560

BL-65

The BL-65 EDAC documented in Technical Basis for the Effective DAC for Th232 Stored in 

Building 65, Rev 0, October 20, 1995 (SRDB 3547). The technical basis shows that the activity 
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2006 (Rev. 2) June 23, 2014

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of Th-230 is insignificant (< 3%) compared to the other isotopes in this particular mixture (see 

Attachment B of SRDB 3547). In addition, its DAC is higher than the effective DAC calculated. 

Therefore, the Th-230 is ignored. The other long-lived isotopes are assumed to be in 

equilibrium. Thus, Th-232, Ra-228, Ac-228, Th-228, and Ra-224 are each assumed to 

represent 20% of the activity. The resulting EDAC based on total activity is 2.22E-12 μCi/ml. 

Dose Reconstructors should multiply the reported number of BL-65 DAC-hours by 2.22E-12 

μCi/ml/DAC and the breathing rate in ml/hour to get the total intake. They then should multiply 

the total intake by 0.2 to get the intakes of Th-232, Ra-228, Ac-228, Th-228, and Ra-224, as 

follows:

• Th-232: intake (μCi) = reported DAC-hrs × 2.22E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.20

• Ra-228: intake (μCi) = reported DAC-hrs × 2.22E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.20

• Ac-228: intake (μCi) = reported DAC-hrs × 2.22E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.20

• Th-228: intake (μCi) = reported DAC-hrs × 2.22E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.20

• Ra-224: intake (μCi) = reported DAC-hrs × 2.22E-12 μCi/ml/DAC × 1.2E+06 ml/hr × 0.20

KS-65

The K-65 silos contained high concentrations of radium-bearing wastes from former production 

activities. The activity fractions for the two K-65 silos are documented in Table 5-16 of ORAUTTKBS-0017 Rev 00 (ORAUT 2004) and appear in Tables E-3 and E-4, below.

Table E-3, Isotopic Composition of K-65 Silo 1

Isotope Activity Activity

Fraction

U-total 1.68 nCi/g 1.61E-03

Ac-227 7.67 nCi/g 7.36E-03

Pb-210 202 nCi/g 1.94E-01

Po-210 281 nCi/g 2.70E-01

Ra-226 477 nCi/g 4.58E-01

Th-228 2.28 nCi/g 2.19E-03

Th-230 68.9 nCi/g 6.62E-02

Th-232 1.11 nCi/g 1.07E-03

Table EA-4, Isotopic Composition of K-65 Silo 2

Isotope Activity Activity

Fraction

U-total 2.37 nCi/g 3.04E-03

Ac-227 6.64 nCi/g 8.50E-03

Pa-231 4.04 nCi/g 5.17E-03
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Pb-210 190 nCi/g 2.43E-01

Po-210 231 nCi/g 2.96E-01

Ra-226 263 nCi/g 3.36E-01

Th-228 7.36 nCi/g 9.42E-03

Th-230 76.2 nCi/g 9.75E-02

Th-232 0.99 nCi/g 1.26E-03

The EDAC that was designated “KS-65” was not located in the documentation. Calculations 

were made for each of the silos using the Equation 1, above.

The resulting EDACs for total activity were 3.2E-11 μCi/ml and 2.0E-11 μCi/ml for Silos 1 and 2, 

respectively. Using the higher of the two would produce the most favorable intakes. Therefore, 

Dose Reconstructors should multiply the reported number of KS-65 DAC-hours by 3.2E-11 

μCi/ml/DAC and the breathing rate in ml/hour to get the total intake. They then should multiply 

the total intake by the respective activity fractions in the above tables. Two calculations will be 

necessary since not only are the activity fractions different, but also Table E-4 contains Pa-231 

in addition to the isotopes in Table E-3.

The calculations are as follows:

Silo 1

• U-total:intake(μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 1.61E03

• Ac-227: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

7.36E-03

• Pb-210: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

1.94E-01

• Po-210: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

2.70E-01

• Ra-226: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

4.58E-01

• Th-228: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

2.19E-03

• Th-230: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

6.62E-02

• Th-232: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

1.07E-03

Silo 2
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• U-total: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 3.04E03

• Ac-227: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

8.50E-03

• Pa-231: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

5.17E-03

• Pb-210: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

2.43E-01

• Po-210: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

2.96E-01

• Ra-226: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

3.36E-01

• Th-228: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

9.42E-03

• Th-230: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

9.75E-02

• Th-232: intake (μCi) = reported DAC-hrs × 3.2E-11 μCi/ml/DAC × 1.2E+06 ml/hr × 

1.26E-03

CELL-8 

The Onsite Disposal Facility (OSDF) was used to dispose of wastes, such as contaminated soil 

and building rubble that were too low-level to justify sending off site. The OSDF was filled in 

sections, called cells. The waste would have been characterized prior to being placed in the 

cells. Cell 8 was the last cell filled. The final cap of cell 8 was installed in 2006. There are only 

2 results in HIS-20 with this EDAC designation, comprising less than 0.01% of the results. The 

results are for 2 individuals on 9/6/2005. Both wore respirators and both results were below the 

minimum detectable DAC-hours shown in the HIS-20 records. Neither individual is a claimant. 

It is suggested that the method for addressing this EDAC be deferred since it may never be 

needed.

RT-210

The remaining EDAC, RT-210, comprises only 1.7% of the results. There were two Radon 

Treatment (RT) Systems. Because of the relatively small number of results, it is assumed that 

the RT-210 results apply to workers at the treatment systems. The first system was a 

temporary arrangement constructed around 2001 that was used to lower radon emissions from 

the K-65 silos while the material was in storage. Little information has been found for this 

system. Construction of the new Radon Control System (RCS) for Silos 1 and 2 (as well as 

some other facilities) was completed and operations began in 2003. The RCS was designed to 

draw radon gas from the headspace inside Silos 1 and 2 and reduce the concentration of gas by 

at least 95 percent to protect workers during removal of the K-65 material. The Silo 1 and 2 
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wastes were removed by slurry, solidified, and placed in casks. The casks were shipped to an 

off-site facility for disposal.

The date range for RT-210 is 2001-2006, which covers both radon treatment systems. In 2006, 

the Silos 1 and 2 Remediation Facility, Transfer Tank Area (TTA), and Radon Control System 

demolitions were completed.

The following description of the Fernald RCS was located in a Corps of Engineers document:

Centrifugal fans pulled radon-laden gas from the sources through the roughing filters for 

initial particulate daughter removal. The air stream was chilled and dried to enhance the 

dynamic adsorption capacity of the activated carbon. Condensed liquids from the gas 

stream were transferred to shielded holdup tanks until transfer and disposition in the 

Remediation Facility could be completed. There were four carbon beds, each containing 

20,400 kg (45,000 lbs) of carbon. These beds were configured so that any two of the 

four beds were in use at any given time. This allowed for decay time of the alternate two 

beds, whereby no carbon changes were required over the life of the project. The RCS 

reduced radon concentration to less than 2% of the inlet concentration and the carbon 

bed outlet air was either recycled to the silos or exhausted through the 46-m (150-ft) tall 

stack. Approximately four inches of carbon steel shielding was designed and installed 

adjacent to the carbon beds to reduce general area dose rates ... ventilation 

requirements were considered for all tasks where radon concentrations greater than 

0.01 WL are expected in the air in occupied spaces, such as the TTA and RCS 

buildings. (http://www.lrb.usace.army.mil/Portals/45/docs/FUSRAP/NFSS/EI/nfssfeasstudy-techmemo-wdoandfll-2011-07.pdf) 

The Ra-222 decay chain is shown in Figure E-1. During the operation of the facility, the three 

long-lived daughters, Pb-210, Bi-210, and Po-210, built up in the system’s piping and filters. 

These isotopes would have been the concern for worker exposures during shutdowns and 

maintenance (e.g. filter changes). Information from the site indicates that the RT-210 EDAC 

was most likely calculated assuming equilibrium among the three isotopes (SRDB 130226). 

The activity fractions are shown in Table E-5.

Table E-5, Activity Fractions for the RT-210 EDAC

Isotope/Element Activity Fraction

Pb-210 0.333

Bi-210 0.333

Po-210 0.333

Figure E-1, Radon-222 Decay Chain Showing Half Lives
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The following DACs were obtained from 10CFR835, Appendix A:

Pb-210: 1E-10 μCi/ml

Bi-210: 1E-07 μCi/ml

Po-210: 3E-10 μCi/ml

From the DAC values and an activity fraction of 0.333 for each isotope an EDAC of 2.25E-10 

μCi/ml was calculated. Dose Reconstructors should multiply the reported number of RT-210 

DAC-hours by 2.25E-10 μCi/ml/DAC and the breathing rate in ml/hour to get the total intake. 

They then should multiply the total intake by 0.333 to get the intakes of Pb-210, Bi-210, and Po210, as follows:

• Pb-210: intake (μCi) = reported DAC-hrs × 2.25E-10 μCi/ml/DAC × 1.2E+06 ml/hr × 

0.333

• Bi-210: intake (μCi) = reported DAC-hrs × 2.25E-10 μCi/ml/DAC × 1.2E+06 ml/hr × 

0.333

• Po-210: intake (μCi) = reported DAC-hrs × 2.25E-10 μCi/ml/DAC × 1.2E+06 ml/hr × 

0.333

Rn-222

3.82 d

Beta Decay

Alpha Decay

Pb-214

26.8 min

Po-218

3.05 min

Bi-214

19.7 min

Pb-210

22 y

Po-214

1.6E-04 s

Bi-210

5.0 d

Pb-206

Stable

Po-210

138 d
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ATTACHMENT F

Analyses of POTENTIAL Thoron Exposure AT FMPC

 Bryce L. Rich

Introduction: 

From the beginning of FMPC operations in late 1953 until the “completion of the disposition of 

the containerized waste inventory” (ref. 33) there have been uranium and thorium processes 

(Summarized in Table 1 from References 11 through 17) with feed materials and the associated 

waste materials that have resulted in elevated levels of 3.823 day half-life Rn-222 (Radon) and 

56 second half-life Rn-220 (Thoron) plus their particulate daughter products. Radon is the first 

daughter product of Ra-226, which was present in significant quantities in the raffinates from 

processing high uranium-bearing pitchblende ores. The elevated Radon exposure levels at 

FMPC from this source are addressed in reference #10, ORAUT-RPRT-0052. The topic of the 

present paper addresses the potential exposures resulting from elevated levels of Thoron during 

processing and/or storage of thorium at FMPC.

As illustrated in the decay diagram of Th-232 (Figure F-1), thoron is the second daughter 

product of Th-228 and in a couple of weeks, following processing for thorium purification, can be 

considered to be in full equilibrium with the parent Th-228. Th-228 is a third daughter product of 

the long-lived Th-232 and generally in 40-65% equilibrium for materials processed at FMPC. 

(Figure F-2) The degree of equilibrium is dependent upon both 1) the decay of Th-228 without 

replenishment from the 5.7 yr half-life Ra-228 after removal of the thorium daughters and 2) the 

time it takes the Ra-228 to build into equilibrium with Th-232 (Figure F-2). For purposes of this 

analysis 65% equilibrium is assumed as the default [1]. Th-228 is also a first daughter product 

of U-232, which could have been present in small quantities from recycled thorium materials 

from Hanford in the 1977-1979 process, but not in sufficient levels from this source to result in a 

significant change in default defined in this paper [2]. 
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Figure F-1. Th-232 decay diagram, including the Rn-220 (Thoron) decay chain
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Figure F-2. Decay and Buildup of Th-228 and daughters following processing

0 5 10 15 20 25

Time since chemical purification, years

0.1

1

10

100

Activity of Isotopes, % of Equilibrium Value

Th-232

Ra-228 or Ac-228 ingrowth

Original Th-228 decay

Th-228 ingrowth from Ac-228

Total Th-228 or Pb-212

Activity of Natural Thorium Following Removal of Impurities

Minimumum Value of Th-228 is 42% at 4.5 Years

Thoron was present and a portion released during the processing and storage of metric tons of 

a variety of forms of thorium. Though this radioactive gas and its short-lived daughter products 

are present in variable levels as a natural background, elevated levels with those of radon have 

been identified and studied and associated with increased respiratory cancer potential, i.e. 

uranium miner studies and others (ref. #s 1, 2, 3, 4, 6, 7, 9, 20, 21, 22, 23, 24, 25, 26, 27, 28, 

29, 30, 31 & 32). 

The primary focus of the FEMP radiological safety programs (ref. #18 & 19) for thorium was to 

define the thorium air concentrations in air in the work place coupled with in vivo lung counts for 

Thorium, the results of which provided the means of controlling worker exposures to levels 

below the then-current permissible levels. In addition the metric ton quantities of thorium in 

process (with the measured particulate releases) or storage provided sources of elevated thoron 

gas release with its subsequent daughter products. The records (ref 5 & 17) indicate that there 

was an awareness of the potential for exposure to thoron and its daughter products through 
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2006 (Rev. 2) June 23, 2014

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documentation of reported “thoron” measurements and holding of the routine breathing zone 

(BZ) and general area (GA) samples for up to 96 hours to allow the short lived Radon and 

Thoron daughter products to decay. This provided a more meaningful measure of the longlived thorium concentrations (ref. #17). Since air activity sample analyses specifically for 

Thoron daughters are insufficient to directly document the routine concentrations in the work 

places at all times, an approach for bounding the possible workplace concentrations of Thoron 

and daughter products is presented. This section presents the methods and considerations of 

bounding the work place exposures to Thoron and primarily the short-lived daughter products, 

based upon theoretical analyses and conservative assumptions.

Thorium Process Inventories and Thoron Potential: 

During the 35 year operating history of the Fernald site, approximately 70% of those years (24 

years) involved the production of 10s to 100s of MTTh parts and products on an annual basis 

for a total of over 3800 MTTh (Table F-1). The production of that quantity of products required 

processing of approximately 4200 MTTh, and leaving over 750 MTTh of scrap and waste 

materials (See Tables F-1 and F-5). On the surface this appears to be a large amount, although 

the primary material processed at FMPC was uranium. Several historical texts refer to amounts 

of thorium being “minor” in nature, since the mass of thorium was generally less than 1% of the 

mass of Recycled Uranium receipts alone. Still the tens to hundreds of metric tons of thorium in 

most of the FMPC facilities at any given time during the operational history was a recognized 

hazard and a source of thoron gas (Rn-220), a very short lived (56 sec) daughter product of Th228. Table F-1 outlines the rough thorium mass balance and estimated inventories during the 

indicated time periods. 

Table F- 1. FMPC Thorium historical mass balance (References 11-17)

Plant Primary 

Buildings

Time 

Period

Quantities (MTTh) * Operations and Materials

Daily Annual Total

Plant 9 1954-

1956

0.5 – 0.6 100-200 380 ThF4 to metal and machining of cores for 

reactors. Wastes stored in Plants 1 & 9 

storage areas.

Plant 4 1954-

1956

0.5 – 0.6 150-300 461 Th oxide conversion to ThF4 for use in 

Plant 9

Plant 6 1959-

1963

0.02 10-20 80 Converted Furnace for Plant 9 1954-56 

Th recovery from scraps and waste.

Plant 1 1954- <1 unk unk Receive, weigh, sample and store source 
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2006 (Rev. 2) June 23, 2014

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1979 and special materials.

Pilot Plant 1954-

1956, 

1964-

1979

0.01 -

0.75

8-381 2558 68% of FMPC Th processed in PP. 

Metal production, Dense thoria, Th nitrate 

to thoria gel, Th hydroxide production, 

processes developed for scale up to 

production levels.

Plant 8 1965, 

1968-

1972

0.025 92 303 ThF4 to Th hydroxide, Th sump cake 

calcined, Th residue processing to Th 

hydroxide

Plant 2/3 1968 0.12 45 45 Short term denitration experiment and 

uranium recovery from thorium hydroxide 

from plant 8.

Total

Processed

3827+ 

plant 1

FMPC waste 

pits

1954-

2006 

closure

na na 65 Discarded Th SS material as waste

For perspective - a metric ton of pure thorium metal at the theoretical density occupies a 

relatively small volume. For example a 10 to 11-gal can (approx. 15” diameter x 15” tall) would 

weigh approximately 1000 lbs or 0.45 MT. Three of these relatively small cans could hold in 

excess of a metric ton of thorium.

As shown above, the processing averages during the 24 years of operation were in the 15

– 20 MTTh per month range or <1 MTTh per day, while process feed stocks (preparatory 

to processing) quantities in the process facilities could have been in the 2 to 15 MT levels, i.e. 

during processing campaigns small quantities were probably placed in the process facilities 

temporarily in queue for the operations [3]. Most of the storage was held in containers in 

adjacent storage buildings as well as barreled wastes held on pads outside the buildings. 
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The primary products were metal cores for the RLO and SRP reactors in 1954-56 and a wide 

range of chemical forms and compounds in the succeeding periods as indicated in Table F-1. 

Process scraps, out-of-spec product, etc. resulted and became a storage and/or process 

category. The processes were also varied, ranging from chemical, metallurgical, metal 

machining, and waste storage, repackaging and shipping. 

The primary process in 1977-79 was unusual in that it was primarily a disposal/storage of 

excess reprocessed thorium materials from Hanford. It involved 6900-gallon tanks of nitrate 

solution from Hanford, each with 10.8 MTTh for conversion to a stable and hence storable thoria 

gel. These tanks were received at a rate of up to two per month for a maximum process rate of 

21.6 MTTh/mo and again <1 per day and with an overall total of 351 MTTh. U-233 was a 

contaminant of the thorium at approximately 130 gm/tank load or approximately 12 ppm Th. 

The total mass of 4.2Kg of U-233 was not separated from the thorium and was stored with the 

thorium (ref 15).

The total mass inventory is only instructive in relation to the thoron inventory when the 

equilibrium ratio of Th-228/Th-232 is known in addition to the fact that thorium-bearing materials 

were seldom 100% thorium. The theoretical activity of Th-232 is 1.09E+5 pCi/g, but for 

consistency with other reports, including the safety analysis report for the thorium storage 

facility, a specific activity for Th-232 and it daughters of 0.989E+5 pCi/g of thorium materials will 

be used as an upper limit, which accounts for lesser densities of thorium compounds and other 

materials in the product. 

The equilibrium age of the thorium processed at FMPC ranged from recently separated to one 

or two years since separation of the non-thorium daughters [1]. Figure F-2 illustrates the 

disequilibrium that occurs when thorium is separated from or purified from its daughter 

elements. Rn-220 is a daughter of the 1.9 yr Th-228, which decreases to approximately 65% of 

equilibrium with Th-232 in 1 year following separation of the radium and actinium daughter 

elements and 43% in 5 years post separation. Full Th-232/Th-228 isotopic equilibrium can be 

assumed for long term storage materials after 35 years or so. 65% will be assumed for the 

functional period, which represents a material 6 mos. to a year after separation and should be 

adequately conservative. Assuming 65% equilibrium would make Rn-220 inventory equivalent 

to 0.64E+5 pCi/g of Th-228 compounds in the processes, and assuming full equilibrium with 

each of its daughters. 

Thorium Waste Repository Locations and Quantities:

FEMP was appointed the DOE thorium materials repository in 1972 and thorium processing was 

shutdown in 1979. During the storage period up to 1500 MTTh were stored pending final 

disposal off site in Nevada and Utah. The repository Thorium wastes and surplus thorium 

materials were accumulated from Fernald and other sites in the repository era from 1972 until 

the “completion of remediation and the disposition of the containerized waste inventory” or final 
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2006 (Rev. 2) June 23, 2014

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closure in 2006 (ref. 33). See Table F-2 for a tabulated summary as of 1987of 13,329 drums of 

thorium plus 184 metric tons of thorium in bulk powders/granules or liquid. Over 689 MTTh 

were stored in the Pilot Plant warehouse and 747 MT in four other designated storage buildings. 

The first shipment from this inventory was to the EnviroCare facility in Utah.

Table F-2. Thorium Storage Inventory in 1987 in Metric Tons of Thorium [FMPC History refs. 

11-17].

Plant 

Area

Storage 

Bldg. #

Drums Net Weight-lbs Th Weight-lbs % Th MTTh

1 67 5992 426978 333044 78 151

5 65 5599 2492505 711210 29 323

65W 240 105032 92955 89 42

8 Silo/Bins Bulk Mtl 50 175

9 64 181 128345 123141 96 56

Pilot 

Plant

68 1317 971398 745785 77 338

Liquid 

Tank

Nitrate 

Solution

na 351

Total 13329 1436

Factors to Consider in Determining Potential Alpha Energy Concentration (PAEC):

PAEC and PAEE Definitions – The primary dose from Thoron is to the respiratory tract organs 

and is delivered primarily by the short-lived daughter products (Table F-3). Due to the short 

radiological half lives and lung clearance of the particulate daughter products there are no 

practical bioassay measurements to define intake (ref. 8, 9, 20, 24,& 32). Thus the method of 

choice for dose evaluation is to measure the Potential Alpha Energy Exposure (PAEE), which is 

the Potential Alpha Energy Concentration in air (PAEC) x the time the worker was exposed. 

The PAEC is measured in Working Levels (WL) and the PAEE is measured in Working Level 

Months (WLM). The bounding defaults recommended in this section are listed as WLM, which 

are directly related to total alpha energy exposure.

Table F-3. Potential Alpha Energy Concentration (PAEC) for Thoron and its Daughters 
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2006 (Rev. 2) June 23, 2014

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Isotope Half-life Atoms/7.5 pCi α MeV/atom PAEC MeV per 

7.5 pCi

Rn-220 56 sec 23 14.6 335

Po-216 0.15 sec <1 Incl -

Pb-212 10.64 hr 15476 7.8 1.21E+5

Bi-212 60.6 min 1469 7.8 0.12E+5

Po-212 0.3 μsec - Incl -

Tl-208 3 min 73 no α -

Total 1.33E+5

Air Monitoring – From the beginning of operations in the early 1950’s the radiological safety 

program evaluated Rn-222 plus daughter products in work areas with specific Radon and 

Radon daughter measurements. The health and safety staff was aware of thoron dose potential 

as evidenced by a number of samples and references to specific Thoron analyses, which have 

been recovered or mentioned in staff reports (ref. 5, 17). During the period following 1989, 

when Westinghouse assumed the contractor roll for FEMP, extensive and recorded radon and 

thoron monitoring was performed across the site (ref. 5). Air monitoring for particulate activity 

was also performed throughout the production period, and enough air sampling data has been 

recovered for realistic conclusions/assumptions related to exposure potentials. 

Work Place Control Functions (FMPC History refs. 11-17) – To better understand the 

workplace ventilation dynamics and air movements, Table F-4 is provided as a summary of the 

dimensions of the buildings in the FMPC complex which handled thorium in any amount. The 

process ventilation systems, which include an air moving system for maintaining a negative 

pressure within the process equipment, a “bag house” particulate filter (a few liquid scrubbers 

were also used), and individual stacks for release of filtered air to the environs. It was reported 

that there were a total of 94 of these ventilation systems/stacks during the early time periods, 

the number of which changed with changing processes and projects. A total of 114 ventilation 

systems is indicated in Table F-4 and the total stack flow for each building is a summary of all 

the individual stack flows in that building. Though there were some general building vents for 

assistance in temperature reduction, these were not used continuously. The air supply for the 

stack discharge flows came from the building working environs around the containment 

systems, which in turn enclosed the process equipment. The pressure differential maintained 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

the air flow into the equipment in which the thorium was being processed. As indicated in Table 

F-4 the air changes per hour for the entire facility volume would average approximately 3 when 

all the individual ventilation systems were operating. Obviously the air change rate in the 

immediately vicinity of the individual processes would be higher.

Table F-4. Building dimensions and Ventilation Systems 

Building Dimensions Volume Volume Number of Total Total 

feet ft3 Ventilation Stack Facility 3 m Systems ft3

/min Chgs/hr

1 100x160x60 9.6E+5 2.72E+4 15 6.1E+4 3.8

2/3 60x380x67 1.53E+6 4.33E+4 6 3.2E+4 1.3

4 225x165x94 3.49E+6 9.88E+4 12 4.38E+4 0.8

5 650x100x52 3.38E+6 9.57E+4 17 1.5E+5 2.7

+ bldg 55 60x30x51 0.92E+5 2.61E+3 1 4.0E+3 2.6

6 500x200x39 3.9E+6 11.0E+4 6 1.35E+5 2.1

7 110x80x114 1.0E+6 2.83E+4 4 1.7E+4 1.0

8 60x260x48 7.49E+5 2.12E+4 24 8.22E+4 6.6

9 300x225x40 2.7E+6 7.65E+4 4 7.89E+4 1.8

Pilot 210x235x54 2.66E+6 7.53E+4 9 4.37E+5 9.9

Plant

64 50x320x22 3.52E+5 1.0E+4 8 1.6E+4 2.7

65 50x210x22 2.31E+5 0.65E+4 8 1.6E+4 4.2

Ave/Total 5E+4 ave 114 total 3.3 ave.

Release Fraction of Stored Materials – Four examples are provided to address the release 

fraction of both Rn-222 and Rn-220 gasses and provide a basis for estimating the release 

fraction (RF) of radon gases to the work environs:

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1- In order to bound the release of radon gas from a source of stored barrels of known waste 

concentration, measurements taken in a shipping car (~6E+4 liter volume) with 48 barrels of 

raffinate wastes with a Ra-226 concentration of 400 nCi/gm were used. This is the maximum 

measured isotopic characterization of silo waste – determined at a much later date. A level of 

approximately 25 Ci of Ra-226 was calculated as the inventory in the 48 drum waste shipment. 

The maximum measured Rn-222 daughter concentration (the highest of a number of samples) 

in the transport carrier was 400 pCi/l in the unventilated shipping car. Using these values, the 

de facto Rn-222 release fraction (RF) from the drums is calculated to be 400 pCi/l ÷ (2.5E+13 

pCi/6E+4 l) = 1E-6. These shipping containers were “enclosed containers” – but obviously not 

vapor tight. This is a measurement of Rn-222 with a 3.8 day half-life and the associated higher 

diffusion capabilities, compared to Rn-220, which would have shown a much lower RF.

2 - Another example and specifically for short-lived thoron gas release is found in the maximum 

measured Rn-220 daughter levels in Building 65 (0.7E+4 m3

) in 1996. Building 65 is one of the 

primary DOE repository storage facilities and the maximum of many measurement 

concentrations was 267 pCi/l. Assuming this measurement was the daughter products of Rn220, the Rn level would be 1.3E+4 pCi/l . See ref. 2 SRDB 27376 and the discussion of the 

choice of “Fraction of equilibrium – Feq of 0.02 in the “Equilibrium of Thoron and daughter 

products Pb-212, Bi-212, Po-212 and Tl-208 discussion.”) The facility contained approximately 

421 MTTh at the time of the measurement with the associated 27 Ci of Rn-220. Part of the 

containers had not been double packed and the lower level drums were in poor repair - 

corroded and leaking. Total release of the Rn-220 inventory would result in 2.7E+13 

pCi/0.7E+7 l = 4E+6 pCi/l for an RF of 1.3E+4/4E+6 = 3E-3. There are many unknowns in this 

example: ventilation of the building, fraction of the stored material containers that were 

breached, location of the air sample in relation to leaking drums, etc. Hence it will not be used 

as a quantitative example – other than to indicate that the RF for some storage facility 

operations will be in the E-3 range and is more likely to be comparable to the storage silo 

example below.

3 - A third example can be demonstrated through measurements made at the top of the Plant 8, 

3000 ft3 storage silo (an elevated cylinder, 17’ dia. x 23’ high with conical sections on the bottom 

and top) with approximately 85 MTTh. Thorium oxide and hydroxide granular material at 

approximately 50% thorium and a measured density of 200 lbs/ft3 in the top of the oxides, 

providing a thorium density of 100 lbs/ft3

. An air activity concentration of 71 WL was measured 

at the top of the tank, which had a 15 foot high x 17 foot diameter air space in the tank above 

the thorium materials (1E+05 l). The conical-shaped surface area of the top (center conveyordeposited) thorium material was calculated as approximately 350 ft2

. 

• With a diffusion distance of approximately 2 cm (ref. 1 and assumed 1 inch), the effective 

thoron quantity available for diffusion to the head space was calculated as: 

• 350 ft2 x 1/12 ft x 100 lbs/ft3 x 454 gm/lb x 0.64E+05 pCi/gm = 8.5E+10pCi 

• This compares to 85 MTTh x 6.4E+10 pCi/MTTh = 5.4E+12 pCi in the total silo or 1.6% of 

the Rn-220 available for release.

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2006 (Rev. 2) June 23, 2014

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• The maximum Rn-220 in the 1E+05 liter head space volume expected is 8.5E+10 pCi/E+05 

l = 9E+5 pCi/l (Total Rn-220 in 1 inch of the surface)

• This is compared to a measured 71 WL= 375 pCi/l Rn-220 /WL [4] 71 WL = 3E+4 pCi/l . 

• This results in an effective RF of 3E+4/9E+5 = 3E-02 – of that within 1” of surface. 

• Hence the RF considering the total Rn-220 (from 85 MTTh) in the silo is 

3E+4/(5.4E+12/1E+5) = 6E-4 

From this example we see that the plant 8 storage silo is essentially a big barrel of thorium and 

the amount of Rn-220 in the head space will be in the order of E-3 to E-4 of the total in the 

container. Migration of the Rn-220 from the container (big or small) to the work environs will be 

in the E-6 range (reasonably estimated, based upon Rn-222 migration from barrels of waste).

4 - The fourth example is found in the Plant 8 elevated double bin storage tanks. Similar to the 

silo example above, a lesser RF is calculated – further verifying the conservatism in the 

assumptions.

Therefore, it is judged to be conservative to use an RF of 1E-6 for stored inventories in intact 

but unsealed containers (10 to 50 gal drums, etc.) and 1E-04 for areas immediately in the 

vicinity of open thorium materials such as silo storage or leaking drums in closed buildings, etc. 

Release Fraction of Materials in Process – For process areas the RF can be conservatively 

calculated based upon general thorium particulate air activity, compared to the total thorium 

material in process. Routine air sampling in the operating areas recorded thorium 

concentrations ranging from tens to a few samples in the tens of thousands of d/m/m3 and 

mostly in the very early 1954-5 period when processes were being developed. Thus it could be 

assumed that a 1 MT (1E+6 g) daily process load in a 5E+4 m3 volume process building in 

which process releases had resulted in 1E+4 d/m/m3

. However, it is not reasonable to assume 

that the air concentrations in the building will be at the maximum levels throughout the entire 

area, and these levels will be assumed to exist in a 20’ hemispherical air space near the 

process equipment (475 m3

). This is based upon the fact that the higher value air samples used 

were undoubtedly BZ samples taken during high level maintenance, e.g. clean out evolutions, 

etc. For these reasons it is reasonable to assume that the air samples represented maximum 

concentrations in the immediate vicinity of the equipment and not of average building 

concentrations.

1E+6 g (0.64E+5 pCi/g) (2.22 dpm/pCi)/475m3 = 0.3E+9 d/m/m3 concentration in the 

air – if all of the process materials were completely released. 

RF = 1E+4/0.3E+9 = 3E-5 

Some injection operations (dumping barrels of feed material into hoppers, etc.) could be 

expected to release the free Thoron in the head space of the container, which would be a ratio 
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2006 (Rev. 2) June 23, 2014

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of 2 cm to the height of the materials in the container – in the range of 0.1 to 0.01 as indicated in 

the discussion of release fractions from stored materials. Even then the particulate dusts 

generated would serve as an absorption/removal mechanism of the daughter products and clear 

in a short period of time (limiting the exposure time). An RF of 0.01 will be assumed. There 

was a variety of process equipment that was used, including liquid extraction vessels, furnaces, 

mixers, etc. all of which were designed for containment. 

Equilibrium of Thoron and daughter products Pb-212, Bi-212, Po-212 and Tl-208 – Quoting

from Harley, New York University School of medicine, (ref. 2) “The inhaled solid decay products 

of thoron deposited on the lung airways deliver the bronchial dose.” And “---the Feq (fraction of 

equilibrium) cannot exceed 0.04 and calculations of Feq for indoor radon and thoron confirms 

the values of 0.4 and 0.02. The value of Feq for thoron is supported by two large data bases, 

one reported by NIRS with measurements in China and one reported by NYU in residences and 

also at the former uranium processing facility at Fernald, OH.” (ref. #3) Pillai and Paul reported 

on the Equilibrium of Thoron and its daughters in a monazite processing plant in India values of 

0.002-0.007. (ref. #4) 0.02 will be used in this analysis as adequately bounding.

Summary Production Rate and Available Thoron Inventory for Release – As indicated 

above the average daily production rate was <1 MTTh (ranging from 0.03 – 0.8) with 6E-02 Ci 

Thoron. Temporary storage within the production facilities during processing campaigns could 

be 5 – 15 MTTh with the associated 0.3 – 0.9 Ci Thoron. DOE long term storage at FMPC was 

100 – 450 MTTh in any of the storage facilities with the associated 6 – 27 Ci Thoron.

Occupancy Time – The nature of storage facilities results in a minimal occupancy time for 

required functions, i.e. 500 hours per year (or 3 months) is assumed for routine storage 

conditions, including required repackaging. For long term storage of high integrity storage 

containers 1 month/year is assumed. The time of occupancy during production periods will be 

assumed as 1750 hrs per year, since an average 1 MTTh continuous production rate will be 

assumed. At 1MTTh daily rate the recorded annual quantities processed would be completed in 

just a fraction of a year. 

Demonstrated Local Diffusion Factor – It has been demonstrated that for Thoron daughter 

concentrations, the concentrations are approximately a factor of 10 higher near the source of 

the release than the concentration at a distance of 3 ft (ref. #6). Since this is probably 

ventilation dependent, this demonstrated reduction factor to the breathing zone of workers will 

be ignored.

Respiratory Protection – It was established practice to wear respiratory protection during 

processing large volumes/masses of hazardous materials. The wearing of respirators would 

remove essentially all of the daughter products, through filtration and electrostatic attraction in 

the filter. However, in the interest of favorability to the claimant due to a few recorded cases of 

procedure violation (there were sample sheets and other logs that made note of personnel not 
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2006 (Rev. 2) June 23, 2014

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wearing masks), it will be assumed that no respirators were worn. The notes themselves 

indicate an unusual condition. Hence this is an admitted overly conservative assumption based 

upon both 1) the established protection policies and practices and 2) demonstrated difference in 

calculated intakes of thorium based upon air monitoring results compared to in vivo measured 

lung burdens.

Summary Assumptions: 

• Materials in process – average <1 MT per day and <400 MT per annum.

• Materials in process facilities in temporary storage – 2 to 15 MT, 15 assumed.

• Long term DOE storage – 100 to 450 MT in any given storage location, 450 assumed.

• Specific activity of Thoron in thorium materials at Fernald – 0.64E+5 pCi/g, e.g. Th228/Th-232 = 0.65

• Facility volume – the facilities were large (averaging 5E+4 m3

). In the interest of 

conservatism, we assume that the mixing or exposure volume will be near the process 

equipment and represent approx. 20 foot radius, hemispherical volume in the total facility 

(475 m3 ).

• RF in temporary or long term storage – 1E-6.

• RF in temporary open storage or with compromised containers – 1E-3 to 1E-4.

• RF in general process areas – 1E-5; 1E-4 will be used in plant 9 during process 

development period in 1954-5.

• Equilibrium factor (Feq) for thoron is 0.02. In a plant configuration with large buildings and 

engineered ventilation, the recommended 0.02 is judged to be conservative. In this case, it 

would require a concentration of Rn-220/Po-216 at 375 pCi/l to produce Pb-212/Bi-212 

concentrations at 7.5 pCi/l and hence result in 1 WL. 

• Diffusion factor of Thoron daughters from source release point – no reduction assumed. 

Fraction of daughter products near source compared to 3 ft away – 0.1, 1 assumed

• Occupancy time in storage facilities – 500 hours per annum – 1 month for long term storage.

• Occupancy time in process facilities – 1750 hours per annum max.

• Protective respiratory protection – no protective equipment will be assumed.

• Thoron WL = 7.5 pCi/l with 100% equilibrium with daughters = 1.3E+5 MeV/l See Table F-3. 

WL = 375 pCi/l Rn-220 + Po-216 to produce measured daughter products Pb-212 + Bi-212 

at 7.5 pCi/l. (See the discussion of Feq factor 3. and summary item 9 above.)

Table F-5. Summary of Thoron Exposure Estimates

Location 

& Time 

Available 

Thoron 

Reduction 

& 

Eff. 

Facility 

Rn220/PoPb212/BiWLM Per 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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Period Activity Calculation 

Factors

Volumeliters *216 

Activity

212 

Activity

year

1954-

1955 

Plant 9 & 

Plant 4

1 MTTh /day =

6.4E+10 pCi 

Rn-220 per day 

in process

RF 1E-4

Feq 2E-2 

Focc.10.2mo 

per yr

5E+5 12.8pCi/l 0.034 WL 0.35 WLM

15 MTTh/day =

1E+12 pCi Rn220 available 

for release to 

process facility

RF 1E-6

Feq 2E-2 

Focc. 2.9mo 

per yr

5E+5 2 pCi/l 5.3E-3 

WL 0.016WLM

1959-

1963

Plant 6

0.02MTTh/day 

= 1.3E+09 pCi 

Rn-220/day in 

process

RF 1E-5

Feq 2E-2 

Focc 10.2mo 

per yr

5E+5 0.026pCi/l 3.5E-3 

WL

ns WLM 

2 MTTh/day =

1.3E+11 pCi 

Rn-220 

available for 

release to 

process facility 

RF 1E-6

Feq 2E-2 

Focc. 2.9mo 

per yr

5E+5 0.26 pCi/l nsWL ns WLM

1965 & 

1968-

1972

Plant 8

0.03 MTTh/day

= 2E+09 pCi 

Rn-220/day in 

process

RF 1E-5

Feq 2E-2 

Focc 10.2mo

5E+5 0.04 pCi/l ns WL ns WLM

2 MTTh/day =

1.3E+11 pCi 

Rn-220 

available for 

RF 1E-6

Feq 2E-2 

Focc. 2.9mo 

5E+5 0.26pCi/l ns WL ns WLM
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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Page 133 of 146

release to 

process facility

per yr

1954-

1956 

&1964-

1979

Pilot

Plant

0.8 MTTh/day 

=5E+10pCi/day 

in process

RF 1E-5

Feq 2E-2 

Focc 10.2mo

5E+5 1 pCi/l 0.0027 

WL

0.027 

WLM

15 MTTh/day =

1E+12 pCi Rn220 available 

for release to 

process facility

RF 1E-6

Feq 2E-2 

Focc. 3 mo 

per yr

5E+5 2 pCi/l 0.0053WL 0.016 

WLM

1954-

1989

Various 

Storage 

Sites

300 MTTh =

2E+13 pCi Rn220 source 

term in Storage 

Facilities

RF 1E-4

Feq 2E-2 

Focc. 3 mo 

per yr

1E+7 200pCi/l 0.53WL 1.55WLM

1972-

2006 

Final 

Closure 

Storage

300MTTh

2E+13 pCi 

Storage 

Facilities

RF 1E-4

Feq 2E-2 

Focc. 1 

mo/yr

1E+7 200 pCi/l 0.53WL 0.53WLM

* For maximization purposes the mixing of the thoron and daughters during the processing of 

thorium is assumed to be in a 20’ hemispherical volume immediately around the release point, 

which in turn is assumed to be the process work station and for the short term stored thorium in 

the process facilities. For long term storage facilities the volume of the storage facilities was 

used. 

Estimates of possible exposures to Thoron indicate that for some periods and in some locations 

(primarily long term storage areas in which some extended work periods were required) 

exposures could be as high as 1.6WLM per year. The work could involve activity with poorly 

ventilated facilities with open containers, such as repackaging failed containers, preparing for 

shipment, etc. Even though release factors (RF) are relatively small for both storage 

configurations and operational conditions and the short half-life of Rn-220 limits the diffusion 

range in all materials to 2 cm or less possible quantities and exposures can still be of concern. 

Reference 9 indicates that due to the relatively longer half lives of the daughter products of 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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Thoron as compared to Radon, significant dose can be experienced with relatively small WLM 

exposures. 

Table F-6 provides a summary of the WLM intake of Rn-220 daughters that could have occurred 

during processing of thorium. The 1.6 WLM estimate for work in the storage facilities in 

preparing thorium materials with higher integrity containers and preparations for shipment is 

conservative. The amount of materials being handled at a given time is not 300 MTTh – and 

would more likely be at least two orders of magnitude less. It is also an overestimate to assume 

that the work would require the indicated work load for the 17 year storage period. In addition 

the work was recognized as requiring special controls, including protective clothing and 

ventilation. It would be appropriate to account for the fact that work with the materials in storage 

were “special project” episodes in nature and would not require more than a fraction of full time.

Table F-6. Thoron Exposure Recommendations 

Time Period* Plant WLM intake each year 

during period 

1954-1956 Plant 9 & 4 0.4

1959-1963 Plant 6 No sig. dose

1965 & 1968-1972 Plant 8 No sig. dose 

1977-1979 Pilot Plant 0.03

1972 - 1989 Storage facilities, 

repackaging, etc.

1.6

1972-2006 Closure Various Storage 0.5

*The time periods listed are primarily recorded operational periods. Time periods not 

specifically included in the 1950s and 1960s could logically be assigned 0.5 WLM as a 

conservative accounting for materials in storage.

Since specific work location of individual workers cannot be determined from the records, it 

would be appropriate to a) make a determination of a claimant as “possibly worked in process 

areas” or b) “not assigned in process areas.” Doses could then be assigned conservatively to 

workers in the “process area” in the 1954-1971 period of 0.4 WLM/yr, in the 1972-1989 period of 

1.6 WLM/yr, and in the 1990-2006 period of 0.5 WLM/yr. Workers not assigned to process 

areas would have no significant potential for Thoron related exposure.

Attributions and Annotations:
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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[1] Rich. Bryce L. ORAU Team. Senior Health Physicist. Thorium feed materials were 

received from a variety of separations facilities stockpiles. A 1 yr delay since separation 

was judged to be a reasonable average. For purposes of thoron intake estimates, an 

assumption of as many as 3 separations of the thoron feed-materials will produce a 

claimant favorable result, while a 65% equilibrium value will provide the claimant 

favorable estimate of Thoron levels.

[2] Rich, Bryce L . ORAU Team. Senior Health Physicist. The U-233 and trace quantities 

of U-232 came from Thorium from Hanford in the 1977-79 period. The thorium was 

“recycled thorium” with a contamination level of approximately 130 gram U-233 per 10.8 

MTTh. The total U-233 plant inventory spread through the 351 MTTh was approximately 

4.2 kg. Trace levels of U-232 could have been present.

[3] Rich, Bryce L. ORAU Team. Senior Health Physicist. The quantities stored in the 

process buildings of 15 MTTh awaiting immediate processing is not known from records 

or interviews. It is reasonable (based upon a knowledge of processing practices) to 

move materials to a ready point and the amount assumed is considered adequately 

conservative. The primary storage locations were outside on pads or in adjoining 

storage facilities. 

 [4] Rich, Bryce L. ORAU Team, Senior Health Physicist. The Working Level is defined in 

terms of the Potential Alpha Energy Concentration (PAEC), resulting from 7.5 pCi. In 

the case of Thoron there is a Feq of 0.02 with the daughter products (See ref. 2), which 

makes the Rn-220 pCi of 375. 

References: 

Primary References:

1. Banjanac, R. et.al, Physics, Chemistry and Technology, Vol. 4, 2006, pp. 93-100 – 

reference for mean diffusion distances for Radon and Thoron, Ref ID 130327

2. Harley, Naomi, et.al., MPM-B.4 Abstract. Radon and Thoron Equilibrium Factors: 

Calculation and Experimental Values – direct quotes. Ref ID 27376

3. Harley, N.H., Measurement of Radon, Thoron, Isotopic Uranium and Thorium to 

Determine Occupational and Environmental Exposure and Risk at Fernald Feed 

Material Production Center, September 15 to March 31, 2004. Ref ID 93957 

4. Pillai, P., and Paul, A., Studies on the Equilibrium of Rn-220 (Thoron) and its 

Daughters in the atmosphere of a Monazite Plant and its Environs, Radiation Protection 

Dosimetry, 1999 Ref ID 27226

5. Weaver, A.S. Memo to H.D. Christiansen, WMCO:EH(HP):87:0112, Radon and Thoron 

Sampling Results, May 1987 Ref ID 4248

6. Stranden, E. Thoron and Radon Daughters in Different Atmospheres, Health Physics 

Vol. 38, May 1980, reference to miners lung cancer locations . Ref ID 130402
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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7. West, C., An Evaluation of the Health Physics Problems from Thorium and its 

Daughters in a Thorium Purification and Fabrication Process, Health Physics, Vol. 8,

1962. Ref ID 107443

8. Allen, D., Lung Dose Conversion Factor for Thoron WLM, OCAS-TIB-0011, Rev. 2, 

1/13/2006 Ref ID 22409

9. Sources and Effects of ionizing Radiation, UNSCEAR, 1977. Ref ID 130321

10. Jesson, K., et.al. Feed Materials Production Center Internal Dose Topics. ORAUTRPRT-0052, Rev. 00-C, 05/18/2011, Ref ID 99554

FMPC Histories:

11. Dolan and Hill, Addendum to FMPC – 2082, Special UC – 11, History of FMPC 

Radionuclide Discharges, December 1988 Ref ID 2165

12. Technical Summary of the Thorium Handling Project, Plant 8, FMPC, January 29, 1988 

Ref ID 33896

13. Mead, J. et.al., History of the Operation of the Feed Materials Production Center by 

NLO, Inc. Ref id 2165

14. FMPC- UC-702, WMCO/DOE 22 Report, Addendum to FMPC-2082 History of FMPC 

Radionuclide Discharges, March 1989, 3/31/89 Ref ID 26096 

15. Grumski, J.T. memo with attachments to Cohen, N., WMCO:WE:87-162, FMPC 

Thorium Storage/Disposition Status Report, May 29, 1987, Ref ID 84398

16. Bogar, L.C., memo to Reafsnyder, J.A., Storage of U-233 at the FMPC, October 21, 

1987, Ref ID 91772

17. Starkey, R.E., letter to Quigley, J.A., M.D., IH&R Department Monthly Report for April, 

1964, May 8, 1964 Ref ID 29540

Others Used:

18. ORAUT-TKBS-0017-5, 5/28/2004, Fernald Environmental Management Project – 

Occupational Internal Dose Ref ID 19485 

19. Tomes, T, Technical Basis for Internal Dosimetry at the Fernald Closure Project, Rev 

No. 2A, 1/4/01, SD-2008 Ref ID 3292 

20. Bodansky, et. al., Indoor Radon and its Hazards, 1987, University of Washington Press, 

Ref ID 130321

21. Durcik, M. & Havlik, F., Experimental Study of Radon and thoron Diffusion Through 

Barriers, Journal of Radioanalytical and Nuclear Chemistry, Vol. 209, No. 2 (19960, 

Feb. 22, 1996 Ref ID 130410 

22. Kotrappa, et.al., Diffusion Coefficients for Unattached Decay Products of ThoronDependence on Ventilation and Relative Humidity, Health Physics, Vol. 31, 1976 Ref ID 

130388

23. Duggan, M., Some Aspects of the Hazard from Airborne Thoron and its Daughter 

Products, Health Physics, Vol. 24, 1973 Ref ID 130398

24. Evans, R. & Goodman, C., Determination of the Thoron Content of Air and its Bearing 

on Lung Cancer Hazards in Industry, republished in Health Physics, Vol. 38 1980 Ref 

ID 27524 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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25. Stranden, E., Thoron (Rn-220) Daughter to Radon (Rn-222) daughter Ratios in 

Thorium-rich Areas, health Physics, Vol. 47, 1984 Ref ID 130406

26. Wiegand, J & Feige, S., Thoron: Ignored and Underestimated in the Big Shadow of 

Radon – and Example from China, Geofisica Internacional (2002), Vol. 41, Num. 3. Ref 

ID 130328

27. Gohel, C. et.al., Estimation of Effective Dose Equivalent from Inhalation of Thoron and 

its Daughter Products at a Thorium Plant, radiation Protection Dosimetry, 1991 Ref ID 

27225

28. Doi, M, et.al, Spatial Distribution of Thoron and Radon Concentrations in the Indoor Air 

of a Traditional Japanese Wooden House, Health Physics, 1993 Ref ID 130401

29. Ma, J, et.al., Influence of Air Flow on the Behavior of Thoron and its Progeny in a 

Traditional Japanese House, health Physics, 1996 Ref ID 130396 

30. Doi, M. and Kobayashi, S., Characterization of Japanese Wooden Houses with 

Enhanced Radon and Thoron Concentrations, Health Physics, 1993 Ref ID 18213 

31. Luetzelschwab, J. and Googins, S., radioactivity Released from Burning Gas Lantern 

Mantles, Health Physics, Vol. 46, 1984. Ref ID 130397 

32. Strom, D.J. AND Reif, R. H., Occupational Exposure to Radon and Thoron, PNNL – 

14108, January 1996 Ref ID 129178 

33. 2006 Fernald Site Environmental Report, May 2007, Ref ID 129793

ATTACHMENT G

Fernald Example Dose Reconstructions for Advisory Board - 2014

Employee 1
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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Page 138 of 146

Cancer Description: Lung (ICD-9: 162); diagnosed 12/31/2013

Bone (ICD-9: 170.2); diagnosed 12/31/2013

Prostate diagnosed (ICD9 185); diagnosed 12/31/2013

BCC, face (ICD-9: 173); diagnosed 12/31/2013

Year of birth: 1939

Gender: Male

Ethnicity: White, non-Hispanic

Smoking History: Former Smoker

Employment Information

Employer: Fernald

Start date: 1/01/1986

End date: 12/31/1988

Occupation: Chemical Operator – worked with thorium

Bioassay: In Vivo Data 

Date Facility Plant Th (mg) Ac-228 (nCi) Pb-212 (nCi) Th-232 (nCi)

6/11/1986 MIVRML 9 0.09 0.04

5/18/1987 MIVRML 9 0.07 -0.04 

6/15/1988 MIVRML 9 0.08 0.05

Based on DL information below, all in vivo counts are negative, < DL, so only missed thorium 

dose is assigned (From Attachment B.1):

Bias and DL for Ac-228 and Pb-212 (nCi)
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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Year Pb-212 

Bias

Pb-212 

DL 

Ac-228 

Bias

Ac-228 

DL

1986 -0.085 0.128 0.020 0.114

1987 -0.047 0.123 0.008 0.106

1988 0.002 0.181 0.058 0.107

Example DR Evaluated Organs

Cancer aInternal Organ 

Lung Lung

Bone Bone Surface

Prostate HNM

b

Skin, BCC Skin

a. SRDB Ref ID: 121336 (ORAUT-OTIB-5)

b. BCC=Basal Cell Carcinoma

Missed thorium dose based on chest count measurements:

The DL for Pb-212 for last chest count measurement (06/15/1988) is 0.181 nCi; the MDA is 2 X 

DL or 0.362 nCi.

The DL for Ac-228 for last chest count measurement (06/15/1988) is 0.107 nCi, the MDA is 2 X 

DL or 0.214 nCi.

For missed dose calculation, Use 1⁄2 of the chest count MDA.

The Pb-212 chest burden was evaluated using the Th-228 biokinetic model in IMBA. This is the 

intake rate for Th-228.

Assign the intake rate for Th-232 using the triple-separated ratio for Th-228 : Th-232 (0.19 : 1). 

Since this is triple separated thorium, there is no Ra-228 intake associated with the thorium 

intake.

The Ac-228 chest burden was evaluated using the Ra-228 biokinetic model in IMBA. This is the 

intake rate for Ra-228. Because this is unsupported Ra-228, it is not part of the thorium 

mixture, and only absorption Type M is assessed. 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

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Page 140 of 146

No correction factors were applied in this example; however, it is assumed that correction 

factors would be applied for non-comp claims since the thorium intake based on a chest count 

would be a slight underestimate.

Employee 1 - Summary of Derived Intake Estimates (pCi/day)

Radionuclide Type M Type S

Th-228 31.548 10.616

Th-232 166.042 55.874

Ra-228 (unsupported) 17.052 Not Applicable

From Attachment F:

Thoron exposure summary 

Radionuclide Time Period Exposure Rate 

(WLM/yr) 

Rn-220 1986-1988 1.6a,b

a. Values are assigned as a constant distribution.

b. Applicable to Lung only (DCAS-TIB-11).

Employee 1 – Material Type Comparison

Organ Thorium

Type M (rem)

Thorium

Type S (rem)

Thoron

(rem)

Lung 25.651 24.786 29.760

Bone 601.436 17.613

Prostate 1.396 0.046

a

Skin, BCC 1.390 0.044

a.BCC=Basal Cell Carcinoma

Employee 1 –Summary of Probability of Causation (POC)a,b
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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POC (%) Lung Bone Prostate Skin

Type M 55.99 92.78 1.28 1.64

Type S 54.08 27.21 0.04 0.05

a. A triangular distribution was assigned in IREP for missed thorium dose based on in vivo 

counts and a constant distribution was assumed for thoron dose to the lung. 

b. Combined POC was not evaluated; organs were independently assessed for comparative 

purposes.

Employee 2

Cancer Description: Lung (ICD-9: 162); diagnosed 12/31/2013

Bone (ICD-9: 170.2); diagnosed 12/31/2013

Prostate diagnosed (ICD9 185); diagnosed 12/31/2013

BCC, face (ICD-9: 173); diagnosed 12/31/2013

Year of birth: 1939

Gender: Male

Ethnicity: White, non-Hispanic

Smoking History: Former Smoker

Employment Information

Employer: Fernald

Start date: 1/01/1986

End date: 12/31/1988

Occupation: Chemical Operator – worked with thorium

Bioassay: None

Because the Chemical Operator worked with thorium, and no bioassay results existed, thorium 

coworker intakes are assigned, as well as the thoron exposure.

From Attachment C (in development): 
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

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Derived Thorium-232 intakes, (pCi/day) 

Period Type M GSDa Type S GSDa

1986-1988b 1.01 7.95 0.220 7.04

a. GSD = Geometric Standard Deviation.

b. These intakes do not represent the finalized values, actual values are in development.

From Attachment F:

Thoron exposure summary 

Radionuclide Time Period Exposure Rate 

(WLM/yr) 

Rn-220 1986-1988 1.6a,b

a. Values are assigned as a constant distribution.

b. Applicable to Lung only (DCAS-TIB-11).

Employee 2 – Material Type Comparison

Organ Thorium

Type M (rem)

Thorium

Type S (rem)

Thoron

(rem)

Lung 0.153 0.096 29.760

Bone 3.655 0.067

Prostate 0.008 <0.001

a

Skin, BCC 0.008 <0.001

a. BCC=Basal Cell Carcinoma

Employee 2 –Summary of Probability of Causationa,b

POC (%) Lung Bone Prostate Skin

Type M 40.77 50.94 0.09 0.09
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2006 (Rev. 2) June 23, 2014

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Type S 40.13 1.40 0.00 0.00

a. A GSD was assigned in IREP for thorium coworker doses and a constant distribution 

was assumed for thoron dose to the lung.

b. Combined POC was not evaluated; organs were independently assessed for 

comparative purposes.

 

Employee 3

Cancer Description: Lung (ICD-9: 162); diagnosed 12/31/2013

Bone (ICD-9: 170.2); diagnosed 12/31/2013

Prostate diagnosed (ICD9 185); diagnosed 12/31/2013

BCC, face (ICD-9: 173); diagnosed 12/31/2013

Year of birth: 1939

Gender: Male

Ethnicity: White, non-Hispanic

Smoking History: Former Smoker

Employment Information

Employer: Fernald

Start date: 1/01/1990

End date: 12/31/2000

Occupation: Chemical Operator – worked with thorium

Bioassay: Thorium BZ air monitoring results (1995-2000), no bioassay for 1990-

1994 employment

Page 

# Date Year Nuclide

Sol. 

Class

Resp 

Type

Corrected 

Dac-hrs

MDI 

DacHrsDachrs Location
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been reviewed to identify and redact 

any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for distribution.

Page 144 of 146

Because the Chemical Operator did not have any bioassay results during his 1990-1994 

employment, thorium doses were assigned based on a thorium intake from air limit calculation 

of 10% Th-232 DAC for 1990-1994. For 1995-2000, his BZ air monitoring results were used to 

assign thorium doses. 

Inhalation and Ingestion intake rates based on 10% of Th-232 DAC 

From Attachment F:

Timeframe Inhalation Rate Ingestion Rate 

58 12/26/1995 1995 Th-230 W Full-Face 0.002 0.027 0.1

PILOT 

PLANT

61 3/30/2000 2000 Th-230 W Full-Face 0.025 0.025 1.272 BLDG 91A

62 10/11/2000 2000 Th-230 W Full-Face 0.011 0.029 0.55 GRID 31A

62 12/18/2000 2000 Th-230 W Full-Face 0.022 0.034 1.121 BLDG 91A

62 12/20/2000 2000 Th-230 W Full-Face 0.01 0.03 0.506 BLDG 91A

62 12/28/2000 2000 Th-230 W Full-Face 0.015 0.034 0.761 BLDG 91A

58 1/15/1996 1996 Th-232 W Full-Face 0.1 0.138 5 

PILOT 

PLANT

59 5/16/1996 1996 Th-232 W PAPR 0.027 0.01 27 BLDG 13A

59 5/17/1996 1996 Th-232 W PAPR 0.053 0.008 53 BLDG 13A

61 7/18/2000 2000 BL-13 W 

PAPR 

HEPA 0.002 0.003 2.017 BLDG 13
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been reviewed to identify and redact 

any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for distribution.

Page 145 of 146

(dpm/yr) (dpm/yr)

1990-1994 266.4 5.55

From Attachment E:

Thoron exposure summary 

Radionuclide Time Period Exposure Rate 

(WLM/yr) 

Rn-220 1990 - 2000 0.5a

a. Values are assigned as a constant distribution. 

b. Applicable to Lung only (DCAS-TIB-11).

For the 1995-2000 BZ air monitoring results, the corrected DAC-hrs (by radionuclide) and (by 

year) were summed. The summation of these results were then converted from DAC-hrs to a 

unit of intake (pCi), and then doses calculated, with the most claimant favorable material type 

selected. (See also DAC-Hr Conversion workbook and EDAC_Bl13_2000 files within Example 

3 folder).

Employee 3 – Material Type Comparison

Organ Thorium

Type M (rem)

Thorium

Type S (rem)

Thoron

(rem)

Lung 0.029 0.140 34.100

Bone 1.535 0.128

Prostate 0.003 <0.001

a

Skin, BCC 0.003 <0.001

a.BCC=Basal Cell Carcinoma

Employee 3 – Summary of Probability of Causationa,b

POC (%) Lung Bone Prostate Skin
White Paper Fernald Dose Reconstruction Methodology for the Post Special Exposure Cohort (SEC) Period, 1979-

2006 (Rev. 2) June 23, 2014

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This information has been reviewed to identify and redact 

any information that is protected by the Privacy Act Privacy Act 5 USC §552a and has been cleared for distribution.

Page 146 of 146

Type M 42.53 3.15 0.000 0.000

Type S 42.60 0.26 0.000 0.000

a. A constant distribution was assigned in IREP for thorium doses based on 10% DAC and for 

thoron dose to the lung. Positive BZ air monitoring results were assigned as a lognormal 

distribution with a GSD of 3.

b. Combined POC was not evaluated; organs were independently assessed for comparative 

purposes.